lib/glcomp: squash warnings from GTK headers

Equivalent change to that in !2495.¹

¹ https://gitlab.com/graphviz/graphviz/-/merge_requests/2495

diff --git a/lib/glcomp/Makefile.am b/lib/glcomp/Makefile.am
index 10ee8defb3837f0acc1b48c1ef12b7c3844c7d52..747508deaf7a0a1fbf06c775596c16128f847070 100644 (file)
--- a/lib/glcomp/Makefile.am
+++ b/lib/glcomp/Makefile.am
@@ -3,7 +3,7 @@
 AM_CPPFLAGS = \
        -I$(top_srcdir)/lib \
        -I$(top_srcdir)/lib/common \
-       $(GTK_CFLAGS) $(GLUT_CFLAGS) $(GTKGL_CFLAGS) $(GTKGLEXT_CFLAGS) $(GLADE_CFLAGS) $(FREETYPE2_CFLAGS) $(XRENDER_CFLAGS)
+       $(GTK_CFLAGS:-I%=-isystem%) $(GLUT_CFLAGS) $(GTKGL_CFLAGS) $(GTKGLEXT_CFLAGS) $(GLADE_CFLAGS) $(FREETYPE2_CFLAGS) $(XRENDER_CFLAGS)
 
 if WITH_SMYRNA
 noinst_HEADERS = glcompbutton.h glcompdefs.h glcomplabel.h \