Prevent ccache from checking the compiler modification time (#25540)

By default ccache includes the compiler mtime and ctime in its hash.
But we use the compiler version as the key for the CircleCI cache step,
so different compiler versions will never share a cache. This will
prevent a mismatch across jobs.

Author: dschuff

.circleci/ccache.conf

@@ -1,2 +1,3 @@
 debug = true
 debug_level = 1
+compiler_check = none