Rename the metric for incremental compile time, so that it's separate…

… from the one for full compile time.

extras/benchmark/run_benchmarks.py

@@ -286,7 +286,7 @@ def run_incremental_compile_benchmark(self):
         start = timer()
         self.run_make_build()
         end = timer()
-        result = {'compile_time': end - start}
+        result = {'incremental_compile_time': end - start}
         return result
 
     def run_runtime_benchmark(self):