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/u_process.c

@@ -135,6 +135,23 @@ __getProgramName()
 }
 
 #    define GET_PROGRAM_NAME() __getProgramName()
+#elif defined(WIN32)
+static const char *
+__getProgramName()
+{
+   static const char *progname;
+   if (progname == NULL) {
+      static char buf[MAX_PATH];
+      GetModuleFileNameA(NULL, buf, sizeof(buf));
+      progname = strrchr(buf, '\\');
+      if (progname)
+         progname++;
+      else
+         progname = buf;
+   }
+   return progname;
+}
+#        define GET_PROGRAM_NAME() __getProgramName()
 #endif
 
 #if !defined(GET_PROGRAM_NAME)