Index: libcxx/CMakeLists.txt
===================================================================
--- libcxx/CMakeLists.txt
+++ libcxx/CMakeLists.txt
@@ -504,7 +504,7 @@
   remove_flags(-DNDEBUG -UNDEBUG -D_DEBUG
                -lc++abi)
 endif()
-remove_flags(-stdlib=libc++ -stdlib=libstdc++)
+remove_flags(--stdlib=libc++ -stdlib=libc++ --stdlib=libstdc++ -stdlib=libstdc++)
 
 # FIXME: Remove all debug flags and flags that change which Windows
 # default libraries are linked. Currently we only support linking the
Index: libcxxabi/CMakeLists.txt
===================================================================
--- libcxxabi/CMakeLists.txt
+++ libcxxabi/CMakeLists.txt
@@ -248,6 +248,8 @@
   # See: https://gitlab.kitware.com/cmake/cmake/issues/19227
   set(CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES "")
   # Remove -stdlib flags to prevent them from causing an unused flag warning.
+  string(REPLACE "--stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+  string(REPLACE "--stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   string(REPLACE "-stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   string(REPLACE "-stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()
Index: libunwind/CMakeLists.txt
===================================================================
--- libunwind/CMakeLists.txt
+++ libunwind/CMakeLists.txt
@@ -323,6 +323,8 @@
 if (LIBUNWIND_HAS_NOSTDINCXX_FLAG)
   list(APPEND LIBUNWIND_COMPILE_FLAGS -nostdinc++)
   # Remove -stdlib flags to prevent them from causing an unused flag warning.
+  string(REPLACE "--stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+  string(REPLACE "--stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   string(REPLACE "-stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   string(REPLACE "-stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()