crt: __p___argv.c: Do not depend on stdlib.h

In followup change will be definition of __argv in stdlib.h changed and
will not use __MINGW_IMP_SYMBOL(__argv) anymore.

So declare __MINGW_IMP_SYMBOL(__argv) in __p___argv.c file manually.

Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-crt/misc/__p___argv.c

diff --git a/mingw-w64-crt/misc/__p___argv.c b/mingw-w64-crt/misc/__p___argv.c
index 8e1f8ed..bb3e456 100644
--- a/mingw-w64-crt/misc/__p___argv.c
+++ b/mingw-w64-crt/misc/__p___argv.c
@@ -4,8 +4,11 @@
  * No warranty is given; refer to the file DISCLAIMER.PD within this package.
  */
 
-#include <stdlib.h>
+#include <_mingw.h>
 
+extern char ***__MINGW_IMP_SYMBOL(__argv);
+
+char ***__cdecl __p___argv(void);
 char ***__cdecl __p___argv(void)
 {
     return __MINGW_IMP_SYMBOL(__argv);