Respect user's pkg-config
--- a/Makefile
+++ b/Makefile
@@ -6,8 +6,9 @@ DISTRIB_DIR= gkrellm-imonc-$(VERSION)
 #
 #
 
-GTK_INCLUDE = $(shell pkg-config gtk+-2.0 --cflags)
-GTK_LIB = $(shell pkg-config gtk+-2.0 --libs)
+PKG_CONFIG ?= pkg-config
+GTK_INCLUDE = $(shell ${PKG_CONFIG} gtk+-2.0 --cflags)
+GTK_LIB = $(shell ${PKG_CONFIG} gtk+-2.0 --libs)
 
 FLAGS = -fPIC $(GTK_INCLUDE)
 LIBS = $(GTK_LIB)