[gimp] build/windows: strengthen `windres` call.

[Jehan Pagès <jehanp src gnome org>]

commit 2c6a53351ab88e4e3a134b3068df25dd8a4168ce
Author: Jehan <jehan girinstud io>
Date:   Thu Dec 31 18:35:07 2015 +0100

    build/windows: strengthen `windres` call.

 build/windows/gimprc-plug-ins.rule |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/build/windows/gimprc-plug-ins.rule b/build/windows/gimprc-plug-ins.rule
index ade2452..6967e93 100644
--- a/build/windows/gimprc-plug-ins.rule
+++ b/build/windows/gimprc-plug-ins.rule
@@ -2,10 +2,12 @@
 
 GIMPPLUGINRC = $(top_builddir)/build/windows/gimp-plug-ins.rc
 
+# `windres` seems a very stupid tool and it breaks with double shlashes
+# in parameter paths. Strengthen the rule a little.
 %.rc.o:
        $(WINDRES) --define ORIGINALFILENAME_STR="$*$(EXEEXT)" \
                --define INTERNALNAME_STR="$*" \
-               --define TOP_SRCDIR="$(top_srcdir)" \
-               -I$(top_srcdir)/app \
-               -I$(top_builddir)/app \
+               --define TOP_SRCDIR="`echo $(top_srcdir) | sed 's*//*/*'`" \
+               -I"`echo $(top_srcdir)/app | sed 's%/\+%/%'`" \
+               -I"`echo $(top_builddir)/app | sed 's%/\+%/%'`"\
                $(GIMPPLUGINRC) $@