[compiler-rt] On Darwin, link all frameworks with -fapplication-extension

[zaks.anna]

Summary

The ASan dylib as well as other compiler-rt dylibs work with app extensions, so we should add -fapplication-extension to the link line when building them. This will avoid linker warnings when using the dylibs in app extensions.

(APIs unavailable to app extensions are listed here: https://developer.apple.com/library/ios/documentation/General/Conceptual/ExtensibilityPG/ExtensionOverview.html#//apple_ref/doc/uid/TP40014214-CH2-SW6)

[beanz]

LGTM.

Thanks,
-Chris

compiler-rt/trunk/cmake/config-ix.cmake

if(APPLE)
   set(CMAKE_OSX_DEPLOYMENT_TARGET "")
   
   set(DARWIN_COMMON_CFLAGS -stdlib=libc++)
   set(DARWIN_COMMON_LINKFLAGS
     -stdlib=libc++
     -lc++
     -lc++abi)
   
+  check_linker_flag("-fapplication-extension" COMPILER_RT_HAS_APP_EXTENSION)
+  if(COMPILER_RT_HAS_APP_EXTENSION)
+    list(APPEND DARWIN_COMMON_LINKFLAGS "-fapplication-extension")
+  endif()
+
   set(DARWIN_osx_CFLAGS
     ${DARWIN_COMMON_CFLAGS}
     -mmacosx-version-min=${SANITIZER_MIN_OSX_VERSION})
   set(DARWIN_osx_LINKFLAGS
     ${DARWIN_COMMON_LINKFLAGS}
     -mmacosx-version-min=${SANITIZER_MIN_OSX_VERSION})
   set(DARWIN_osx_BUILTIN_MIN_VER 10.5)
   set(DARWIN_osx_BUILTIN_MIN_VER_FLAG