[gimp] configure.ac: fix building screenshot plugin without libXmu

[Nils Philippsen <nphilipp src gnome org>]

commit 51b1775ff7a9337cb7438c6607e92e6e78ee35ba
Author: Nils Philippsen <nils redhat com>
Date:   Thu Oct 7 18:19:24 2010 +0200

    configure.ac: fix building screenshot plugin without libXmu
    
    Set SCREENSHOT_LIBS="$XMU_LIBS" only if libXmu development files are
    available.

 configure.ac |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 5e229dd..5344a64 100644
--- a/configure.ac
+++ b/configure.ac
@@ -956,10 +956,10 @@ if test "$gdk_target" = x11; then
       AC_CHECK_LIB(Xmu, XmuClientWindow,
         [AC_CHECK_HEADERS(X11/Xmu/WinUtil.h,
 	  have_libxmu=yes
-          XMU_LIBS="$X_LIBS $X_PRE_LIBS -lX11 -lXmu -lXt",
+          XMU_LIBS="$X_LIBS $X_PRE_LIBS -lX11 -lXmu -lXt"
+          SCREENSHOT_LIBS="$XMU_LIBS",
 	  [have_libxmu="no (XMU header file not found)"],[#include <gdk/gdkx.h>])],
 	[have_libxmu="no (XMU library not found)"], -lXt -lX11)
-      SCREENSHOT_LIBS="$XMU_LIBS"
    fi
 
    # Check for shaped window extension