Windows MSYS CROSSTOOL: Remove /usr from cxx_builtin_include_directory

After 8b3ba50246fed6ff13d70299fb039cc66be465c4, msys path should not
appear in CROSSTOOL, because Bazel won't translate it anymore.

Fix https://github.com/bazelbuild/bazel/issues/4318

Change-Id: I33d783a2ef14299e586856fefa2d68adce587045
PiperOrigin-RevId: 179667545

tools/cpp/windows_cc_configure.bzl

diff --git a/tools/cpp/windows_cc_configure.bzl b/tools/cpp/windows_cc_configure.bzl
index 5c1ea91..da13691 100644
--- a/tools/cpp/windows_cc_configure.bzl
+++ b/tools/cpp/windows_cc_configure.bzl
@@ -59,8 +59,7 @@
       '   tool_path { name: "gcc" path: "%susr/bin/gcc" }\n' % escaped_msys_root +
       '   cxx_flag: "-std=gnu++0x"\n' +
       '   linker_flag: "-lstdc++"\n' +
-      '   cxx_builtin_include_directory: "%s"\n' % escaped_msys_root +
-      '   cxx_builtin_include_directory: "/usr/"\n' +
+      '   cxx_builtin_include_directory: "%susr/"\n' % escaped_msys_root +
       '   tool_path { name: "gcov" path: "%susr/bin/gcov" }\n' % escaped_msys_root +
       '   tool_path { name: "ld" path: "%susr/bin/ld" }\n' % escaped_msys_root +
       '   tool_path { name: "nm" path: "%susr/bin/nm" }\n' % escaped_msys_root +