gnome-keyring: Don't hard-code pkg-config executable

Helpful if your pkg-config executable has a prefix based on the
architecture, for example.
Signed-off-by: NHeiko Becker <heirecka@exherbo.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

contrib/credential/gnome-keyring/Makefile

@@ -4,12 +4,13 @@ all:: $(MAIN)
 CC = gcc
 RM = rm -f
 CFLAGS = -g -O2 -Wall
+PKG_CONFIG = pkg-config
 
 -include ../../../config.mak.autogen
 -include ../../../config.mak
 
-INCS:=$(shell pkg-config --cflags gnome-keyring-1 glib-2.0)
-LIBS:=$(shell pkg-config --libs gnome-keyring-1 glib-2.0)
+INCS:=$(shell $(PKG_CONFIG) --cflags gnome-keyring-1 glib-2.0)
+LIBS:=$(shell $(PKG_CONFIG) --libs gnome-keyring-1 glib-2.0)
 
 SRCS:=$(MAIN).c
 OBJS:=$(SRCS:.c=.o)