package/prboom: fix build with autoconf >= 2.72

Set ac_cv_type_gid_t=yes to avoid the following build failure raised
since bump of autoconf to version 2.72 in commit
524f3536029dace3ce9aa154d3ca4685582e1955:

In file included from i_network.c:37:
../../config.h:207:15: error: two or more data types in declaration specifiers
  207 | #define gid_t int
      |               ^~~

Fixes: 524f3536029dace3ce9aa154d3ca4685582e1955
 - http://autobuild.buildroot.org/results/0d74517129130e6f26dc8c8aacae175ed8bd4b54

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/prboom/prboom.mk

@@ -6,7 +6,7 @@
 
 PRBOOM_VERSION = 2.5.0
 PRBOOM_SITE = http://downloads.sourceforge.net/project/prboom/prboom%20stable/$(PRBOOM_VERSION)
-PRBOOM_CONF_ENV = ac_cv_type_uid_t=yes
+PRBOOM_CONF_ENV = ac_cv_type_gid_t=yes ac_cv_type_uid_t=yes
 PRBOOM_DEPENDENCIES = sdl sdl_net sdl_mixer
 PRBOOM_LICENSE = GPL-2.0+
 PRBOOM_LICENSE_FILES = COPYING