Replace __cplusplus comparisons and dialect __has_feature checks with TEST_STD_VER.

This is a huge cleanup that helps make the libc++ test suite more portable.
Patch from STL@microsoft.com. Thanks STL!

llvm-svn: 272716
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/capacity.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/capacity.pass.cpp
index c05346a..4b09c09 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/capacity.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/capacity.pass.cpp
@@ -49,7 +49,7 @@
     s.erase(50);
     test(s);
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     S s;
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/clear.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/clear.pass.cpp
index b73af75..e0254c0 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/clear.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/clear.pass.cpp
@@ -39,7 +39,7 @@
     s.erase(50);
     test(s);
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     S s;
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/empty.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/empty.pass.cpp
index ac65f51..fbed5c3 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/empty.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/empty.pass.cpp
@@ -31,7 +31,7 @@
     test(S("123"));
     test(S("12345678901234567890123456789012345678901234567890"));
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     test(S());
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/length.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/length.pass.cpp
index d3ae1aa..13e966dc 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/length.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/length.pass.cpp
@@ -31,7 +31,7 @@
     test(S("123"));
     test(S("12345678901234567890123456789012345678901234567890"));
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     test(S());
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp
index d857be2..fca14dd 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp
@@ -63,7 +63,7 @@
     test(S("123"));
     test(S("12345678901234567890123456789012345678901234567890"));
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     test(S());
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp
index 9c8f679..e92a0e1 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp
@@ -37,7 +37,7 @@
     test(S("123"));
     test(S("12345678901234567890123456789012345678901234567890"));
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     test(S());
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/size.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/size.pass.cpp
index 21b475a..4657aea 100644
--- a/libcxx/test/std/strings/basic.string/string.capacity/size.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/size.pass.cpp
@@ -31,7 +31,7 @@
     test(S("123"), 3);
     test(S("12345678901234567890123456789012345678901234567890"), 50);
     }
-#if __cplusplus >= 201103L
+#if TEST_STD_VER >= 11
     {
     typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
     test(S(), 0);