Port configure script to C99

Related to:

  <https://fedoraproject.org/wiki/Changes/PortingToModernC>
  <https://fedoraproject.org/wiki/Toolchain/PortingToModernC>

gimp-configure-c99.patch

@@ -0,0 +1,56 @@
+Do not call the undeclared exit function.  Implicit function
+declarations are likely not going to be supported by future compilers
+by default, changing the outcome of this configure probe.
+
+Submitted upstream: <https://gitlab.gnome.org/GNOME/gimp/-/merge_requests/810>
+
+diff --git a/configure b/configure
+index 6e62da8e3c164f82..f1c447baf7ff68f7 100755
+--- a/configure
++++ b/configure
+@@ -28898,17 +28898,17 @@ else $as_nop
+ 	  char *shmaddr;
+ 	id = shmget (IPC_PRIVATE, 4, IPC_CREAT | 0600);
+ 	if (id == -1)
+-	  exit (2);
++	  return 2;
+ 	  shmaddr = shmat (id, 0, 0);
+ 	  shmctl (id, IPC_RMID, 0);
+ 	  if ((char*) shmat (id, 0, 0) == (char*) -1)
+ 	  {
+ 	    shmdt (shmaddr);
+-	    exit (1);
++	    return 1;
+ 	  }
+ 	  shmdt (shmaddr);
+ 	  shmdt (shmaddr);
+-	  exit (0);
++	  return 0;
+ 	}
+ 
+ _ACEOF
+diff --git a/configure.ac b/configure.ac
+index d73f56228712f59d..32d2a072863ae64f 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -1284,17 +1284,17 @@ elif test "x$shmtype" = "xsysv"; then
+ 	  char *shmaddr;
+ 	id = shmget (IPC_PRIVATE, 4, IPC_CREAT | 0600);
+ 	if (id == -1)
+-	  exit (2);
++	  return 2;
+ 	  shmaddr = shmat (id, 0, 0);
+ 	  shmctl (id, IPC_RMID, 0);
+ 	  if ((char*) shmat (id, 0, 0) == (char*) -1)
+ 	  {
+ 	    shmdt (shmaddr);
+-	    exit (1);
++	    return 1;
+ 	  }
+ 	  shmdt (shmaddr);
+ 	  shmdt (shmaddr);
+-	  exit (0);
++	  return 0;
+ 	}
+       ]])],
+       [AC_DEFINE([IPC_RMID_DEFERRED_RELEASE],[1],

gimp.spec

@@ -191,6 +191,8 @@ Patch3:         gimp-2.10.18-no-phone-home-default.patch
 # use external help browser directly if help browser plug-in is not built
 Patch100:       gimp-2.10.24-external-help-browser.patch
 
+Patch101:       gimp-configure-c99.patch
+
 %description
 GIMP (GNU Image Manipulation Program) is a powerful image composition and
 editing program, which can be extremely useful for creating logos and other
@@ -277,6 +279,11 @@ EOF
 %patch100 -p1 -b .external-help-browser
 %endif
 
+%patch101 -p1
+
+# Avoid re-running autotools.
+touch -r aclocal.m4 configure*
+
 %build
 # allow python2 package for RHEL-8
 export RHEL_ALLOW_PYTHON2_FOR_BUILD=1