[CMake] Don't use CLANG_DEFAULT_* values

[phosek]

Summary

These are not necessarily correct, just because Clang is configured
to use libc++ or compiler-rt as defaults doesn't mean that the host
compiler uses these as defaults as well. A more correct solution
would be to test the host compiler to check what the default actually
is as attempted in D46857.

PR-38025

[manojgupta]

Thanks Petr, I can confirm that this fixed the compiler-rt build issues in Chrome OS builds.

compiler-rt/CMakeLists.txt

 pythonize_bool(SANITIZER_CAN_USE_CXXABI)
 
 set(SANITIZER_CXX_ABI "default" CACHE STRING
     "Specify C++ ABI library to use.")
 set(CXXABIS none default libstdc++ libc++)
 set_property(CACHE SANITIZER_CXX_ABI PROPERTY STRINGS ;${CXXABIS})
 
 if (SANITIZER_CXX_ABI STREQUAL "default")
-  if (CLANG_DEFAULT_CXX_STDLIB STREQUAL "libc++" AND (TARGET cxx OR HAVE_LIBCXX))
-    set(SANITIZER_CXX_ABI_LIBNAME "libc++")
-    set(SANITIZER_CXX_ABI_INTREE 1)
-  elseif (APPLE)
+  if (APPLE)
     set(SANITIZER_CXX_ABI_LIBNAME "libc++")
     set(SANITIZER_CXX_ABI_SYSTEM 1)
   elseif (FUCHSIA)
     set(SANITIZER_CXX_ABI_LIBNAME "libc++")
     set(SANITIZER_CXX_ABI_INTREE 1)
   else()
     set(SANITIZER_CXX_ABI_LIBNAME "libstdc++")
     set(SANITIZER_CXX_ABI_SYSTEM 1)
   endif()
 else()
   set(SANITIZER_CXX_ABI_LIBNAME "${SANITIZER_CXX_ABI}")
   set(SANITIZER_CXX_ABI_SYSTEM 1)
 endif()
 
 set(COMPILER_RT_RUNTIME "default" CACHE STRING
     "Compiler runtime to use.")
 
 if (COMPILER_RT_RUNTIME STREQUAL "default")
-  if (CLANG_DEFAULT_RTLIB STREQUAL "compiler-rt")
-    set(COMPILER_RT_RUNTIME_LIBRARY "builtins")
-  elseif (FUCHSIA)
+  if (FUCHSIA)
     set(COMPILER_RT_RUNTIME_LIBRARY "builtins")
   endif()
 else()
   set(COMPILER_RT_RUNTIME_LIBRARY "${COMPILER_RT_RUNTIME}")
 endif()
 
 include(config-ix)