rt-tests: Fix build with non-gcc compilers

Makery hard sets CC to be some form of gcc, make it set only if CC
variable is absent in environment.

(From OE-Core rev: 8d83c6ad78e1f965a55c0d3f430bad2781a3eb33)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-rt/rt-tests/files/0001-Makefile-Set-CC-AR-variable-only-if-it-doesn-t-have-.patch

@@ -0,0 +1,30 @@
+From 9640dde4241e1314b8e8ea35b0c8dab0b30ae51f Mon Sep 17 00:00:00 2001
+From: Khem Raj <raj.khem@gmail.com>
+Date: Sun, 3 Jan 2016 10:50:56 -0800
+Subject: [PATCH] Makefile: Set CC/AR variable only if it doesn't have a value
+
+This helps it compile with clang or any other compilers besides gcc
+
+Signed-off-by: Khem Raj <raj.khem@gmail.com>
+---
+Upstream-Status: Submitted
+
+ Makefile | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/Makefile b/Makefile
+index 1e4b7d1..2c2d396 100644
+--- a/Makefile
++++ b/Makefile
+@@ -1,6 +1,6 @@
+ VERSION = 0.96
+-CC=$(CROSS_COMPILE)gcc
+-AR=$(CROSS_COMPILE)ar
++CC?=$(CROSS_COMPILE)gcc
++AR?=$(CROSS_COMPILE)ar
+ 
+ OBJDIR = bld
+ 
+-- 
+2.6.4
+

meta/recipes-rt/rt-tests/rt-tests_0.96.bb

@@ -10,7 +10,8 @@ LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe \
 require rt-tests.inc
 inherit ptest
 
-SRC_URI += "file://run-ptest \
+SRC_URI += "file://0001-Makefile-Set-CC-AR-variable-only-if-it-doesn-t-have-.patch \
+            file://run-ptest \
             file://rt_bmark.py \
            "
 # Do not install hwlatdetect