[jhbuild] simple install: Use CC and CFLAGS from environment

[Frederic Peters <fpeters src gnome org>]

commit cc6591890084bd9509915f29e7c7a485caef0dcf
Author: Marcus Karlsson <mk acc umu se>
Date:   Wed Oct 29 08:44:08 2014 +0100

    simple install: Use CC and CFLAGS from environment
    
    Unlike the MAKE variable both CC and CFLAGS are not taken from the
    environment. Allow these variables to be overridden using environment
    variables.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=739337

 Makefile.plain |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/Makefile.plain b/Makefile.plain
index 316725d..1630781 100644
--- a/Makefile.plain
+++ b/Makefile.plain
@@ -1,8 +1,8 @@
 PACKAGE = jhbuild
 VERSION = 0.1
 
-CC = cc
-CFLAGS = -Wall -O2
+CC ?= cc
+CFLAGS ?= -Wall -O2
 
 MAKE ?= make