[libcxx] [test] Use TEST_COMPILER_C1XX.

Also TEST_COMPILER_CLANG in one place. (More could be changed.)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329977 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed