[libcxx] Use the correct variable name for target triple in lit

[phosek]

Summary

The variable representing target triple in libcxx is named
LIBCXX_TARGET_TRIPLE, not TARGET_TRIPLE.

[beanz]

LGTM.

[phosek]

This is no longer needed after D57670 landed.

test/lit.site.cfg.in

 config.enable_shared            = "@LIBCXX_ENABLE_SHARED@"
 config.enable_32bit             = "@LIBCXX_BUILD_32_BITS@"
 config.cxx_abi                  = "@LIBCXX_CXX_ABI_LIBNAME@"
 config.use_sanitizer            = "@LLVM_USE_SANITIZER@"
 config.sanitizer_library        = "@LIBCXX_SANITIZER_LIBRARY@"
 config.abi_library_path         = "@LIBCXX_CXX_ABI_LIBRARY_PATH@"
 config.configuration_variant    = "@LIBCXX_LIT_VARIANT@"
 config.host_triple              = "@LLVM_HOST_TRIPLE@"
-config.target_triple            = "@TARGET_TRIPLE@"
+config.target_triple            = "@LIBCXX_TARGET_TRIPLE@"
 config.use_target               = len("@LIBCXX_TARGET_TRIPLE@") > 0
 config.sysroot                  = "@LIBCXX_SYSROOT@"
 config.gcc_toolchain            = "@LIBCXX_GCC_TOOLCHAIN@"
 config.generate_coverage        = "@LIBCXX_GENERATE_COVERAGE@"
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.executor                 = "@LIBCXX_EXECUTOR@"
 config.llvm_unwinder            = "@LIBCXXABI_USE_LLVM_UNWINDER@"
 config.has_libatomic            = "@LIBCXX_HAS_ATOMIC_LIB@"
 config.use_libatomic            = "@LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@"
 config.debug_build              = "@LIBCXX_DEBUG_BUILD@"
 config.libcxxabi_shared         = "@LIBCXXABI_ENABLE_SHARED@"
 config.cxx_ext_threads          = "@LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY@"
 
 # Let the main config do the real work.
 config.loaded_site_config = True
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")