xbps-src: enable CCACHE_COMPRESS to save space

Using CCACHE_COMPRESS is transparent. It compresses manifests and object
files in the cache but can read both, compressed and uncompress files.

xbps-src

@@ -614,7 +614,7 @@ else
         export CCACHE_DIR="$XBPS_HOSTDIR/ccache"
         # Avoid not using cached files just due to compiler mtime
         # changes when e.g. bootstrapping
-        export CCACHE_COMPILERCHECK=content
+        export CCACHE_COMPILERCHECK=content CCACHE_COMPRESS=1
         export PATH="$CCACHEPATH:$PATH"
         mkdir -p $CCACHE_DIR
     fi