[libc++] Remove support for specifying LIBCXX_CXX_ABI_SYSTEM manually

This was only kept until Chromium fixed their build of libc++, which
they have now done according to
	https://bugs.chromium.org/p/chromium/issues/detail?id=1067216

diff --git a/libcxx/cmake/Modules/HandleLibCXXABI.cmake b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
index f5d15f8..a62efc0 100644 (file)
--- a/libcxx/cmake/Modules/HandleLibCXXABI.cmake
+++ b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
@@ -104,7 +104,7 @@ if ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libstdc++" OR
 elseif ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi")
   set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_SOURCE_DIR}/../libcxxabi/include")
 
-  if((LIBCXX_CXX_ABI_SYSTEM OR LIBCXX_STANDALONE_BUILD) AND NOT (LIBCXX_CXX_ABI_INTREE OR HAVE_LIBCXXABI))
+  if(LIBCXX_STANDALONE_BUILD AND NOT (LIBCXX_CXX_ABI_INTREE OR HAVE_LIBCXXABI))
     set(shared c++abi)
     set(static c++abi)
   else()