fix incorrect libstdc++ from GCC >= 5.1 check

Assume that libstdc++ from GCC >= 5.1 is being used only when compiling with GCC >= 5.1.

This unbreaks GCC 4.8.5 and 4.9.3 builds after https://codereview.chromium.org/1837563002/
landed.

Review URL: https://codereview.chromium.org/1863523005

Cr-Commit-Position: refs/heads/master@{#385416}


CrOS-Libchrome-Original-Commit: 5c8abdc1aa67ebcfa7f2ecbb41506c65fa2ccc36
1 file changed
tree: 512663444af015b28a0a9ef99e35b22c7f6e73c4
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/