https://patch-diff.githubusercontent.com/raw/J-Lentz/iwgtk/pull/14.patch

--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,8 @@
-CC=gcc
-CFLAGS=`pkg-config --cflags gtk+-3.0`
+CC?=gcc
+CCINCS=`pkg-config --cflags gtk+-3.0`
 LDLIBS=`pkg-config --libs gtk+-3.0`
 
-prefix=/usr/local
+prefix?=$(PREFIX)
 exec_prefix=$(prefix)
 bindir=$(exec_prefix)/bin
 datarootdir=$(prefix)/share
@@ -23,10 +23,10 @@
 .PHONY : clean install uninstall
 
 iwgtk : $(objects)
-	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
+	$(CC) $(CCINCS) $(CFLAGS) -o $@ $^ $(LDLIBS)
 
 %.o : $(srcdir)/%.c $(headers)
-	$(CC) -c $(CFLAGS) -o $@ $<
+	$(CC) -c $(CCINCS) $(CFLAGS) -o $@ $<
 
 $(srcdir)/icons.c : icons.gresource.xml $(icons)
 	glib-compile-resources --target=$@ --sourcedir=icons --generate-source $<
