travis: Use ccache for MinGW builds

scripts/test.sh

@@ -134,6 +134,7 @@ win*)
 	# no make check for Windows binaries unless we run on a windows host
 	if test "$APPVEYOR" != "True"; then
 		TARGET=
+		CCACHE=ccache
 	else
 		CONFIG="$CONFIG --enable-openssl"
 		CFLAGS="$CFLAGS -I/c/OpenSSL-$TEST/include"
@@ -146,12 +147,12 @@ win*)
 	win64)
 		CONFIG="--host=x86_64-w64-mingw32 $CONFIG --enable-dbghelp-backtraces"
 		DEPS="gcc-mingw-w64-x86-64 binutils-mingw-w64-x86-64 mingw-w64-x86-64-dev $DEPS"
-		CC="x86_64-w64-mingw32-gcc"
+		CC="$CCACHE x86_64-w64-mingw32-gcc"
 		;;
 	win32)
 		CONFIG="--host=i686-w64-mingw32 $CONFIG"
 		DEPS="gcc-mingw-w64-i686 binutils-mingw-w64-i686 mingw-w64-i686-dev $DEPS"
-		CC="i686-w64-mingw32-gcc"
+		CC="$CCACHE i686-w64-mingw32-gcc"
 		;;
 	esac
 	;;