Change toolchain includes (#9318)

This fixes path resolution failures when following `#include_next` directives in headers found from paths in `extra_compiler_flags`.

toolchain/BUILD

@@ -150,8 +150,8 @@ cc_toolchain_config(
     bit_flag = "-m32",
     cpp_flag = "-lstdc++",
     extra_compiler_flags = [
-        "-I/usr/lib/gcc/i686-w64-mingw32/8.3-posix/include/c++",
+        "-isystem/usr/lib/gcc/i686-w64-mingw32/8.3-posix/include/c++",
-        "-I/usr/lib/gcc/i686-w64-mingw32/8.3-posix/include/c++/i686-w64-mingw32",
+        "-isystem/usr/lib/gcc/i686-w64-mingw32/8.3-posix/include/c++/i686-w64-mingw32",
         "-fsjlj-exceptions",
     ],
     extra_include = "/usr/lib/gcc/i686-w64-mingw32/8.3-posix/include",
@@ -171,8 +171,8 @@ cc_toolchain_config(
     bit_flag = "-m64",
     cpp_flag = "-lstdc++",
     extra_compiler_flags = [
-        "-I/usr/lib/gcc/x86_64-w64-mingw32/8.3-posix/include/c++/",
+        "-isystem/usr/lib/gcc/x86_64-w64-mingw32/8.3-posix/include/c++/",
-        "-I/usr/lib/gcc/x86_64-w64-mingw32/8.3-posix/include/c++/x86_64-w64-mingw32",
+        "-isystem/usr/lib/gcc/x86_64-w64-mingw32/8.3-posix/include/c++/x86_64-w64-mingw32",
     ],
     extra_include = "/usr/lib/gcc/x86_64-w64-mingw32/8.3-posix/include",
     extra_linker_flags = [

toolchain/cc_toolchain_config.bzl

@@ -134,10 +134,11 @@ def _impl(ctx):
                           "-Wall",
                           "-no-canonical-prefixes",
                           "--target=" + ctx.attr.target_full_name,
+                          "-fvisibility=hidden",
+                      ] + ctx.attr.extra_compiler_flags + [
                           "-isystem",
                           ctx.attr.toolchain_dir,
-                          "-fvisibility=hidden",
+                      ],
-                      ] + ctx.attr.extra_compiler_flags,
                   ),
               ],
           ),