autotest-tests: force to use gcc to compile a benchmark

clang could not compile iTLB_benchmark_function.c so we need
to use gcc to build this test. upstream bug filed
https://llvm.org/bugs/show_bug.cgi?id=25416

BUG=chromium:552019
TEST=it uses gcc even CC=clang is set.

Change-Id: I2e0ed115d8cf47687e6bb33ed504eddecc7e3765
Reviewed-on: https://chromium-review.googlesource.com/310977
Commit-Ready: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Reviewed-by: Yunlian Jiang <yunlian@chromium.org>
diff --git a/client/site_tests/hardware_TLBMissCost/src/Makefile b/client/site_tests/hardware_TLBMissCost/src/Makefile
index e1a54b4..115f386 100644
--- a/client/site_tests/hardware_TLBMissCost/src/Makefile
+++ b/client/site_tests/hardware_TLBMissCost/src/Makefile
@@ -1,4 +1,7 @@
 CFLAGS=-O0 -g
+# Force to use gcc to build it. Clang upstream bug is at
+# https://llvm.org/bugs/show_bug.cgi?id=25416
+CC=${CHOST}-gcc
 
 BINS=iTLB_benchmark
 OBJS=iTLB_benchmark.o iTLB_benchmark_function.o