Restore project-specific cmake/test-static-assert.c

This file was wrongly extracted to the .core/build submodule during the
build system extraction. It's a project-specific compile test used by
CMakeLists.txt:185 and must remain in the project tree.

Verified: make configure && make build && make package all pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmake/test-static-assert.c

@@ -0,0 +1,6 @@
+#include <assert.h>
+
+static_assert(1, "FAIL");
+int main(int argc, char *argv[]) {
+	return 0;
+}