Fixing some warnings on Linux

There were only a few warnings left, so I fixed them and enabled the unused variable warning by removing the "-Wno-unused" flag. Only the -Wno-unused-parameter remains for now (could be removed later).
Review URL: https://codereview.chromium.org/12480002

git-svn-id: http://skia.googlecode.com/svn/trunk@8030 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/bench/benchmain.cpp b/bench/benchmain.cpp
index 459f340..b16cca3 100644
--- a/bench/benchmain.cpp
+++ b/bench/benchmain.cpp
@@ -676,10 +676,10 @@
             configName = gConfigs[configIndex].fName;
             backend = gConfigs[configIndex].fBackend;
             GrContext* context = NULL;
-            SkGLContextHelper* glContext = NULL;
             BenchTimer* timer = timers[configIndex];
 
 #if SK_SUPPORT_GPU
+            SkGLContextHelper* glContext = NULL;
             if (kGPU_Backend == backend) {
                 context = gContextFactory.get(gConfigs[configIndex].fContextType);
                 if (NULL == context) {