Compilation: close the linker output file before writing whole cache manifest

Otherwise a different process may get a cache hit on the file while we still
have a writable fd open for it. This isn't actually a real problem in the sense
that running the file should just work as expected if the OS allows it. But
until very recently[0], the Linux kernel would give ETXTBSY in this case. So
make sure we close the file before letting other processes know that it's
usable.

closes https://codeberg.org/ziglang/zig/issues/31563

[0] https://github.com/torvalds/linux/commit/2a010c41285345da60cece35575b4e0af7e7bf44

src/Compilation.zig

@@ -3230,16 +3230,16 @@ pub fn update(comp: *Compilation, main_progress_node: std.Progress.Node) UpdateE
             // cache manifest must not be written.
             if (anyErrors(comp)) return;
 
-            // Failure here only means an unnecessary cache miss.
-            man.writeManifest() catch |err| {
-                log.warn("failed to write cache manifest: {s}", .{@errorName(err)});
-            };
-
             if (comp.bin_file) |lf| {
                 lf.destroy();
                 comp.bin_file = null;
             }
 
+            // Failure here only means an unnecessary cache miss.
+            man.writeManifest() catch |err| {
+                log.warn("failed to write cache manifest: {s}", .{@errorName(err)});
+            };
+
             assert(whole.lock == null);
             whole.lock = man.toOwnedLock();
         },