Revert "[libunwind][CMake] Use libc++ headers when available"

This causing build failure on sanitizer bots because of the unused
argument '-nostdinc++' during linking of libunwind.

This reverts commit 0e14fd1a1d37b9c6d55a2d3bc7649e5b39ce74d3.

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@295202 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ed14e06..3ba4b65 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -282,24 +282,4 @@
 
 include_directories(include)
 
-find_path(
-  LIBUNWIND_LIBCXX_INCLUDES_INTERNAL
-  __libcpp_version
-  PATHS ${LLVM_MAIN_SRC_DIR}/projects/libcxx/include
-        ${LLVM_MAIN_SRC_DIR}/runtimes/libcxx/include
-  NO_DEFAULT_PATH
-)
-if ((NOT LIBUNWIND_STANDALONE_BUILD OR HAVE_LIBCXX) AND
-    IS_DIRECTORY "${LIBUNWIND_LIBCXX_INCLUDES_INTERNAL}")
-  set(LIBUNWIND_CXX_INCLUDE_PATHS_DEFAULT "${LIBUNWIND_LIBCXX_INCLUDES_INTERNAL}")
-endif()
-
-set(LIBUNWIND_CXX_INCLUDE_PATHS "${LIBUNWIND_CXX_INCLUDE_PATHS_DEFAULT}" CACHE PATH
-    "Paths to C++ header directories separated by ';'.")
-
-if (NOT LIBUNWIND_CXX_INCLUDE_PATHS STREQUAL "")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -nostdinc++")
-  include_directories("${LIBUNWIND_CXX_INCLUDE_PATHS}")
-endif()
-
 add_subdirectory(src)