Maker: partially implement configurer cache invalidation

progress towards #35473

build.zig

@@ -268,7 +268,7 @@ pub fn build(b: *std.Build) !void {
         }
 
         // Ensure git version changes get picked up.
-        b.dependOnFileContents(b.graph.path(.build_root, ".git/HEAD"));
+        b.dependOnFileContents(b.path(".git/HEAD"));
 
         const version_string = b.fmt("{d}.{d}.{d}", .{ zig_version.major, zig_version.minor, zig_version.patch });