Dump src/auto/config.mk on Travis CI

Author: splhack

.travis.yml

@@ -26,6 +26,7 @@ before_install:
 script:
   - NPROC=$(getconf _NPROCESSORS_ONLN)
   - ./configure $CONFOPT --enable-fail-if-missing && make -j$NPROC
+  - cat src/auto/config.mk
   - ./src/vim --version
   - make test