Fix Travis bug: Actually use multiple compilers.

.travis.yml

@@ -1,15 +1,23 @@
 language: c
+compiler:
+  - gcc
+  - clang
 env:
   global:
     # The next declaration is the encrypted COVERITY_SCAN_TOKEN, created
     #   via the "travis encrypt" command using the project repo's public key
     - secure: "NEQUeZwTTJ+1Pdy2CpNte1nJLYRY2H8+dpvnGS2HP6U/Ok6ZQm4Zxic+ufhabuymbCV7Jvwwy6Gaj8+ObIDahhzAsiMRXSymnvFHELAnq7DiikJ2HqBvFhPzPI2/vDmEP37msGW1dloipLhdKMeuYYP++BpApnC6KVRVJDXg5JI="
   matrix:
-    - CC="gcc"
-    - CC="gcc -std=c89"
-    - CC="clang"
+    - C89=no
+    - C89=yes
+matrix:
+  exclude:
+    - compiler: clang
+      env: C89=yes
 script: ./configure && make check
-before_script: ./bootstrap.sh
+before_script:
+  - if [ "$CC $C89" = "gcc yes" ]; then export CC="gcc -std=c89"; fi
+  - ./bootstrap.sh
 sudo: false
 
 addons: