[gimp] Issue #3884: missing libgtk-3-dev leads to configure syntax error.

[Jehan <jehanp src gnome org>]

commit 49351777b6bc3abd542a0919ef337b45a46163d2
Author: Jehan <jehan girinstud io>
Date:   Mon Apr 27 12:21:19 2020 +0200

    Issue #3884: missing libgtk-3-dev leads to configure syntax error.

 configure.ac | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index b158f83347..34a1b93f80 100644
--- a/configure.ac
+++ b/configure.ac
@@ -812,9 +812,9 @@ LIBS=$gimp_save_LIBS
 
 AC_PATH_XTRA
 
-PKG_CHECK_MODULES(GTK, gtk+-3.0 >= gtk_required_version,,
-                  [add_deps_error([gtk+-3.0 >= gtk_required_version],
-                                  [Test for GTK+ failed.])])
+# Do not delay GTK errors and exit immediately as it will provoke
+# harder to understand syntax errors of missing autoconf macros.
+PKG_CHECK_MODULES(GTK, gtk+-3.0 >= gtk_required_version);
 
 AC_PATH_PROGS(GTK_UPDATE_ICON_CACHE, gtk-update-icon-cache-3.0 gtk-update-icon-cache, no)
 if test "x$GTK_UPDATE_ICON_CACHE" = xno; then