[libc++] Don't override LIBCXX_CXX_ABI_INCLUDE_PATHS for libcxxrt

When testing libc++ for our cross-compiled CheriBSD target we specify an
explicit LIBCXX_CXX_ABI_INCLUDE_PATHS for libcxxrt. The hardcoded path
/usr/include/c++/v1 was introduced in 61e89737c5daf7b65341936f88f68efb680cdcd4
and overrides any value passed on the CMake command line. Fix this by using
it as a fallback rather than a fixed default value.

Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D82095

diff --git a/libcxx/cmake/Modules/HandleLibCXXABI.cmake b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
index 973d875..5070e99 100644 (file)
--- a/libcxx/cmake/Modules/HandleLibCXXABI.cmake
+++ b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
@@ -102,7 +102,9 @@ if ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libstdc++" OR
     "${_LIBSUPCXX_LIBNAME}" "${_LIBSUPCXX_LIBNAME}" "${_LIBSUPCXX_INCLUDE_FILES}" "bits"
     )
 elseif ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi")
-  set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_SOURCE_DIR}/../libcxxabi/include")
+  if(NOT LIBCXX_CXX_ABI_INCLUDE_PATHS)
+    set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_SOURCE_DIR}/../libcxxabi/include")
+  endif()
 
   if(LIBCXX_STANDALONE_BUILD AND NOT (LIBCXX_CXX_ABI_INTREE OR HAVE_LIBCXXABI))
     set(shared c++abi)
@@ -116,7 +118,9 @@ elseif ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi")
     "-DLIBCXX_BUILDING_LIBCXXABI"
     "${shared}" "${static}" "cxxabi.h;__cxxabi_config.h" "")
 elseif ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxrt")
-  set(LIBCXX_CXX_ABI_INCLUDE_PATHS "/usr/include/c++/v1")
+  if(NOT LIBCXX_CXX_ABI_INCLUDE_PATHS)
+    set(LIBCXX_CXX_ABI_INCLUDE_PATHS "/usr/include/c++/v1")
+  endif()
   setup_abi_lib(
     "-DLIBCXXRT"
     "cxxrt" "cxxrt" "cxxabi.h;unwind.h;unwind-arm.h;unwind-itanium.h" ""