Travis: use -std=gnu99 with NSS, and clang with Chutney

NSS:
* test NSS-specific code with -std=gnu99
* use a recent gcc version from the latest Ubuntu image

Chutney:
* use clang, so we keep one clang Linux job
* keep clang on a fast job, so the overall build finishes quickly

Closes ticket 32500 for 0.3.5.

.travis.yml

@@ -42,13 +42,13 @@ matrix:
       ## Turn off some newer features, turn on clang's -Wtypedef-redefinition
       env: C_DIALECT_OPTIONS="-std=gnu99"
     ## We check NSS
-    ## NSS is a fast job, clang is slower on Linux, so we do NSS clang
-    - env: NSS_OPTIONS="--enable-nss"
-      compiler: clang
-    ## We run chutney on Linux, because it's faster than chutney on macOS
     ## Use -std=gnu99 to turn off some newer features, and maybe turn on some
     ## extra gcc warnings?
-    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" C_DIALECT_OPTIONS="-std=gnu99"
+    - env: NSS_OPTIONS="--enable-nss" C_DIALECT_OPTIONS="-std=gnu99"
+    ## We run chutney on Linux, because it's faster than chutney on macOS
+    ## Chutney is a fast job, clang is slower on Linux, so we do Chutney clang
+    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes"
+      compiler: clang
       ## (Linux only) Use an older Linux image (Ubuntu Trusty)
       ## The Xenial and Bionic images cause permissions issues for chutney,
       ## this is a workaround, until we fix #32240.