[gegl] build: make --without-exiv2 and --with-exiv2 work

[Øyvind Kolås <ok src gnome org>]

commit d452e2ee3913c079fb2b72d8b6c78e3f998d9ea0
Author: Arfrever Frehtes Taifersar Arahesis <Arfrever FTA gmail com>
Date:   Fri Jul 21 23:42:15 2017 +0200

    build: make --without-exiv2 and --with-exiv2 work
    
    bug #779121

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 9867a41..ed7c54b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1121,7 +1121,7 @@ AC_SUBST(LIBSPIRO)
 AC_ARG_WITH(exiv2, [  --without-exiv2         build without libexiv2 support])
 
 have_libexiv2="no"
-if test "x$with_libexiv2" != "xno"; then
+if test "x$with_exiv2" != "xno"; then
   PKG_CHECK_MODULES(EXIV2, exiv2,
     have_exiv2="yes",
     have_exiv2="no  (exiv2 library not found)")