runtime: make fatal failures unrecoverable

Match the Go runtime by terminating for deadlocks, stack overflows,
runtime and GC invariants, invalid lock operations, and platform
initialization failures instead of routing them through panic/recover.

Keep language-level runtime errors and unsupported user operations
recoverable. Add crash coverage that verifies fatal errors bypass deferred
recover calls.

src/runtime/os_windows.go

@@ -29,7 +29,7 @@ func findGlobals(found func(start, end uintptr)) {
 		// it using GetModuleHandle to account for ASLR etc.
 		result := _GetModuleHandleExA(GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT, nil, &module)
 		if gcAsserts && (!result || module.signature != 0x5A4D) { // 0x4D5A is "MZ"
-			runtimePanic("cannot get module handle")
+			runtimeFatal("cannot get module handle")
 		}
 	}