[cmake] [libunwind] Fix find_path() problems when cross compiling

When CMAKE_SYSROOT or CMAKE_FIND_ROOT_PATH is set, cmake
recommends setting CMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY
globally which means find_path() always prepends CMAKE_SYSROOT or
CMAKE_FIND_ROOT_PATH to all paths used in the search.

However, this find_path() invocation is looking for a path in the
libcxx project on the host system, not the target system,
which can be done by passing NO_CMAKE_FIND_ROOT_PATH.

Differential Revision: https://reviews.llvm.org/D41621

llvm-svn: 323141

libunwind/CMakeLists.txt

@@ -329,7 +329,8 @@ find_path(
   PATHS ${LLVM_MAIN_SRC_DIR}/projects/libcxx/include
         ${LLVM_MAIN_SRC_DIR}/runtimes/libcxx/include
   NO_DEFAULT_PATH
-)
+  NO_CMAKE_FIND_ROOT_PATH
+  )
 if ((NOT LIBUNWIND_STANDALONE_BUILD OR HAVE_LIBCXX) AND
     IS_DIRECTORY "${LIBUNWIND_LIBCXX_INCLUDES_INTERNAL}")
   set(LIBUNWIND_CXX_INCLUDE_PATHS_DEFAULT "${LIBUNWIND_LIBCXX_INCLUDES_INTERNAL}")