fix: GIT_COMMIT_HASH forces full rebuilds and defeats compiler caching (#15537)

src/slic3r/GUI/BuildCommit.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+// Read these rather than including git_commit_hash.h, which changes with every
+// commit and rebuilds everything that includes it.
+
+namespace Slic3r { namespace GUI {
+
+// The commit alone, safe to use in a commit URL.
+extern const char *const build_commit_hash;
+
+// The same, with "-dirty" when the build had uncommitted changes. Use this
+// wherever the build is shown to a person.
+extern const char *const build_commit_label;
+
+}} // namespace Slic3r::GUI