Workaround for false -Warray-bounds in Travis

ccache + clang produces a false strcmp warning, see
https://llvm.org/bugs/show_bug.cgi?id=20144

Since this only happens with ccache and --strict-warnings, and
only with certain versions of glibc / clang, disabling
ccache is a reasonable short-term workaround.

Reviewed-by: Richard Levitte <levitte@openssl.org>

.travis.yml

@@ -75,7 +75,7 @@ before_script:
           export CROSS_COMPILE=${CC%%gcc}; unset CC;
           $srcdir/Configure mingw64 $CONFIG_OPTS -Wno-pedantic-ms-format;
       else
-          if which ccache >/dev/null; then
+          if which ccache >/dev/null && [ "$CC" != clang-3.6 ]; then
               CC="ccache $CC";
           fi;
           $srcdir/config $CONFIG_OPTS;