Oh, it turns out there IS a warning for shutting up -pedantic. Woo!

meson.build

@@ -96,6 +96,11 @@ else
 	]
 
 	if libui_OS == 'windows'
+		# -pedantic causes warnings without this, even if a function is explicitly marked __attribute__((format(ms_printf)))
+		# references: https://curl.haxx.se/mail/lib-2012-06/0433.html
+		libui_project_compile_args += [
+			'-Wno-pedantic-ms-format',
+		]
 		# don't require shipping the MinGW-w64 DLLs
 		libui_project_link_args += [
 			'-static',

test/lib/timer_windows.c

@@ -269,15 +269,7 @@ static void redirectToOnTimeout(CONTEXT *ctx, struct timeoutParams *p)
 
 static void criticalCallFailed(const char *func, HRESULT hr)
 {
-// sigh, -pedantic... (TODO)
-#ifndef _MSC_VER
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wformat"
-#endif
 	fprintf(stderr, "*** internal error in timerRunWithTimeout(): %s failed: 0x%08I32X\n", func, hr);
-#ifndef _MSC_VER
-#pragma GCC diagnostic pop
-#endif
 	abort();
 }