Fix gcc warning -Wsign-compare

Add the compile flag '-Wsign-compare' and adapt the code to fix all
cases of this warning.

Change-Id: I26b08fa5a03e4ac294daf697d32cf9140d84350d

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 7fc6198cf..d1c1abdf8 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -247,7 +247,7 @@ Worker::Results Worker::run(std::function<Targets (GoalFactory &)> req)
                        .exclusiveJoin(std::move(onInterrupt.promise));
 
     // TODO GC interface?
-    if (auto localStore = dynamic_cast<LocalStore *>(&store); localStore && settings.minFree != 0) {
+    if (auto localStore = dynamic_cast<LocalStore *>(&store); localStore && settings.minFree != 0u) {
         // Periodically wake up to see if we need to run the garbage collector.
         promise = promise.exclusiveJoin(boopGC(*localStore));
     }