Opportunistically use perftools if installed.

Allows us to collect profiles of the open source build using gprof.
diff --git a/.gitignore b/.gitignore
index 3cae07e..0bde146 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,15 @@
+# C/C++ build outputs
 bins
-coverage
-deps
-*.gcno
 gens
 libs
 objs
+
+# gcov coverage data
+coverage
+*.gcno
+
+# profiler output
+*.prof
+
+# python compiled objects
 *.pyc