travis: disable tautological-compare warnings

.travis.yml

@@ -150,7 +150,8 @@ before_script:
   - 7z x $HOME/srb2_cache/SRB2-v2115-assets-2.7z -oassets
   - mkdir build
   - cd build
-  - export CFLAGS="-Wall -W -Werror"
+  - export CFLAGS="-Wall -W -Werror -Wno-tautological-compare -Wno-error=tautological-compare"
+  - $CC -Wno-error=tautological-compare -dM -E - < /dev/null&>/dev/null||export CFLAGS="Wall -W -Werror"
   - cmake .. -DCMAKE_BUILD_TYPE=Release
 
 before_install: