Merge pull request #6273 from akyrtzi/pr/stable/libcpp-assertions

[stable/20221013][CMake] Use `LLVM_ENABLE_ASSERTIONS` to enable assertions in `libc++`

Author: akyrtzi

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -83,6 +83,10 @@ if( LLVM_ENABLE_ASSERTIONS )
       endforeach()
      endif()
   endif()
+  # Enable assertions in libstdc++.
+  add_compile_definitions(_GLIBCXX_ASSERTIONS)
+  # Enable assertions in libc++.
+  add_compile_definitions(_LIBCPP_ENABLE_ASSERTIONS)
 endif()
 
 if(LLVM_ENABLE_EXPENSIVE_CHECKS)