[libc++] NFC: Clean up a lot of old Lit features

The libc++ test suite has a lot of old Lit features used to XFAIL tests
and mark them as UNSUPPORTED. Many of them are to workaround problems on
old compilers or old platforms. As time goes by, it is good to go and
clean those up to simplify the configuration of the test suite, and also
to reflect the testing reality. It's not useful to have markup that gives
the impression that e.g. clang-3.3 is supported, when we don't really
test on it anymore (and hence several new tests probably don't have the
necessary markup on them).
diff --git a/libcxx/test/std/strings/string.conversions/stod.pass.cpp b/libcxx/test/std/strings/string.conversions/stod.pass.cpp
index 9456d4e..d13b695 100644
--- a/libcxx/test/std/strings/string.conversions/stod.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stod.pass.cpp
@@ -11,11 +11,6 @@
 // double stod(const string& str, size_t *idx = 0);
 // double stod(const wstring& str, size_t *idx = 0);
 
-// When back-deploying to macosx10.7, the RTTI for exception classes
-// incorrectly provided by libc++.dylib is mixed with the one in
-// libc++abi.dylib and exceptions are not caught properly.
-// XFAIL: with_system_cxx_lib=macosx10.7
-
 #include <string>
 #include <cmath>
 #include <cassert>
diff --git a/libcxx/test/std/strings/string.conversions/stof.pass.cpp b/libcxx/test/std/strings/string.conversions/stof.pass.cpp
index 2c8e4c9..22dda0b 100644
--- a/libcxx/test/std/strings/string.conversions/stof.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stof.pass.cpp
@@ -5,10 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-//
-// PR14919 was fixed in r172447, out_of_range wasn't thrown before.
-// XFAIL: with_system_cxx_lib=macosx10.7
-// XFAIL: with_system_cxx_lib=macosx10.8
 
 // <string>
 
diff --git a/libcxx/test/std/strings/string.conversions/stoi.pass.cpp b/libcxx/test/std/strings/string.conversions/stoi.pass.cpp
index 6f27332..b3e4163 100644
--- a/libcxx/test/std/strings/string.conversions/stoi.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stoi.pass.cpp
@@ -11,11 +11,6 @@
 // int stoi(const string& str, size_t *idx = 0, int base = 10);
 // int stoi(const wstring& str, size_t *idx = 0, int base = 10);
 
-// When back-deploying to macosx10.7, the RTTI for exception classes
-// incorrectly provided by libc++.dylib is mixed with the one in
-// libc++abi.dylib and exceptions are not caught properly.
-// XFAIL: with_system_cxx_lib=macosx10.7
-
 #include <string>
 #include <cassert>
 #include <stdexcept>
diff --git a/libcxx/test/std/strings/string.conversions/stol.pass.cpp b/libcxx/test/std/strings/string.conversions/stol.pass.cpp
index ef0cbb4..a05a4b1 100644
--- a/libcxx/test/std/strings/string.conversions/stol.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stol.pass.cpp
@@ -5,10 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-//
-// PR14919 was fixed in r172447, out_of_range wasn't thrown before.
-// XFAIL: with_system_cxx_lib=macosx10.7
-// XFAIL: with_system_cxx_lib=macosx10.8
 
 // <string>
 
@@ -93,9 +89,9 @@
     {
         assert(idx == 0);
     }
-//  LWG issue #2009
     try
     {
+        // LWG#2009 and PR14919
         std::stol("9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }
@@ -105,6 +101,7 @@
     }
     try
     {
+        // LWG#2009 and PR14919
         std::stol(L"9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }
diff --git a/libcxx/test/std/strings/string.conversions/stold.pass.cpp b/libcxx/test/std/strings/string.conversions/stold.pass.cpp
index 19531670..4b1b1b1 100644
--- a/libcxx/test/std/strings/string.conversions/stold.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stold.pass.cpp
@@ -11,11 +11,6 @@
 // long double stold(const string& str, size_t *idx = 0);
 // long double stold(const wstring& str, size_t *idx = 0);
 
-// When back-deploying to macosx10.7, the RTTI for exception classes
-// incorrectly provided by libc++.dylib is mixed with the one in
-// libc++abi.dylib and exceptions are not caught properly.
-// XFAIL: with_system_cxx_lib=macosx10.7
-
 #include <cassert>
 #include <cmath>
 #include <stdexcept>
diff --git a/libcxx/test/std/strings/string.conversions/stoll.pass.cpp b/libcxx/test/std/strings/string.conversions/stoll.pass.cpp
index 73d5e82..bccf845 100644
--- a/libcxx/test/std/strings/string.conversions/stoll.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stoll.pass.cpp
@@ -5,10 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-//
-// PR14919 was fixed in r172447, out_of_range wasn't thrown before.
-// XFAIL: with_system_cxx_lib=macosx10.7
-// XFAIL: with_system_cxx_lib=macosx10.8
 
 // <string>
 
@@ -95,6 +91,7 @@
     }
     try
     {
+        // LWG#2009 and PR14919
         std::stoll("99999999999999999999999999", &idx);
         assert(false);
     }
@@ -104,6 +101,7 @@
     }
     try
     {
+        // LWG#2009 and PR14919
         std::stoll(L"99999999999999999999999999", &idx);
         assert(false);
     }
diff --git a/libcxx/test/std/strings/string.conversions/stoul.pass.cpp b/libcxx/test/std/strings/string.conversions/stoul.pass.cpp
index 6ef8613..c620925 100644
--- a/libcxx/test/std/strings/string.conversions/stoul.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stoul.pass.cpp
@@ -5,10 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-//
-// PR14919 was fixed in r172447, out_of_range wasn't thrown before.
-// XFAIL: with_system_cxx_lib=macosx10.7
-// XFAIL: with_system_cxx_lib=macosx10.8
 
 // <string>
 
@@ -91,9 +87,9 @@
     {
         assert(idx == 0);
     }
-//  LWG issue #2009
     try
     {
+        // LWG#2009 and PR14919
         std::stoul("9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }
@@ -103,6 +99,7 @@
     }
     try
     {
+        // LWG#2009 and PR14919
         std::stoul(L"9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }
diff --git a/libcxx/test/std/strings/string.conversions/stoull.pass.cpp b/libcxx/test/std/strings/string.conversions/stoull.pass.cpp
index 3e21c68..803065c 100644
--- a/libcxx/test/std/strings/string.conversions/stoull.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stoull.pass.cpp
@@ -5,10 +5,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-//
-// PR14919 was fixed in r172447, out_of_range wasn't thrown before.
-// XFAIL: with_system_cxx_lib=macosx10.7
-// XFAIL: with_system_cxx_lib=macosx10.8
 
 // <string>
 
@@ -92,9 +88,9 @@
     {
         assert(idx == 0);
     }
-//  LWG issue #2009
     try
     {
+        // LWG#2009 and PR14919
         std::stoull("9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }
@@ -104,6 +100,7 @@
     }
     try
     {
+        // LWG#2009 and PR14919
         std::stoull(L"9999999999999999999999999999999999999999999999999", &idx);
         assert(false);
     }