[libcxx] Remove custom CMake code targeting Mac OS 10.6

libc++ has dropped support for Mac OS 10.6 for a while, and we don't
have any testers set up for that OS.

This commit puts in an error message so that people can reach out to
the libc++ maintainers in case support for 10.6 is still expected (as
opposed to silently failing in weird ways). We can completely drop
support for 10.6 and remove the error message some time in the future
when we're sure that nobody is relying on it.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@344576 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index e068edc..1fa315b 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -149,14 +149,9 @@
   endif()
 
   if ( CMAKE_OSX_DEPLOYMENT_TARGET STREQUAL "10.6" )
-    add_definitions(-D__STRICT_ANSI__)
-    add_link_flags(
-      "-compatibility_version 1"
-      "-current_version 1"
-      "-install_name /usr/lib/libc++.1.dylib"
-      "-Wl,-reexport_library,/usr/lib/libc++abi.dylib"
-      "-Wl,-unexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++unexp.exp"
-      "/usr/lib/libSystem.B.dylib")
+    message(FATAL_ERROR "Mac OSX 10.6 is not supported anymore as a deployment "
+                        "target. If you need support for this, please contact "
+                        "the libc++ maintainers.")
   else()
 	  if (DEFINED CMAKE_OSX_SYSROOT AND NOT CMAKE_OSX_SYSROOT STREQUAL "")
       list(FIND CMAKE_OSX_ARCHITECTURES "armv7" OSX_HAS_ARMV7)