Hack to ensure core.a looks newer during builds

Commented in the code, but buasically the generation of git version
includes on each build causes the cached core.a to be ignored
because that header is newer than the file we just wrote (even though
on any CI run the GIT version is identical).

Author: earlephilhower

tests/common.sh

@@ -52,6 +52,14 @@ function build_sketches()
         if [ $testcnt -ne $build_rem ]; then
             continue  # Not ours to do
         fi
+
+        # Uber hack warning - setting the cached core.a file to the future to
+        # ensure it is accepted as unmodified during build process.  Problem is
+        # the git version header is rewritten after each compile, so the
+        # builder sees it is new and says "rebuild the whole thing!"
+
+        if [ -e $cache_dir/core/*.a ]; then touch -t 203712310000 $cache_dir/core/*.a; fi
+
         rm -rf $build_dir/*
         local sketchdir=$(dirname $sketch)
         local sketchdirname=$(basename $sketchdir)