[Support][CachePruning] Fix regression in pruning interval

Fixed broken comparison.
borked by: rL284966 (see: https://reviews.llvm.org/D25730).

Differential Revision: https://reviews.llvm.org/D40119

This is a second attempt to commit this.
The first attempt broke lld and gold tests that had been written against
the incorrect behaivour.

llvm-svn: 318524

llvm/lib/Support/CachePruning.cpp

@@ -161,7 +161,7 @@ bool llvm::pruneCache(StringRef Path, CachePruningPolicy Policy) {
       return false;
     }
   } else {
-    if (Policy.Interval == seconds(0)) {
+    if (Policy.Interval != seconds(0)) {
       // Check whether the time stamp is older than our pruning interval.
       // If not, do nothing.
       const auto TimeStampModTime = FileStatus.getLastModificationTime();