util/u_process: implement util_get_process_name for Windows

There's not yet any users of this function on Windows, but it prints a
warning during builds, and seems easy enough to implement. So let's add
a trivial implementation.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7548>

src/util/process_test.c

@@ -52,10 +52,14 @@ expect_equal_str(const char *expected, const char *actual, const char *test)
 static void
 test_util_get_process_name (void)
 {
-   #if !DETECT_OS_WINDOWS
-   const char* name = util_get_process_name();
-   expect_equal_str("process_test", name, "util_get_process_name");
-   #endif
+#if DETECT_OS_WINDOWS
+   const char *expected = "process_test.exe";
+#else
+   const char *expected = "process_test";
+#endif
+
+   const char *name = util_get_process_name();
+   expect_equal_str(expected, name, "util_get_process_name");
 }
 
 /* This test gets the real path from Meson (BUILD_FULL_PATH env var),