dump stack usage of GCC builds as an FYI

With this flag GCC emits text .su files in parallel to each .o.

Change-Id: I17365d921e960d77df74a95149850cb7d123dc6b
Reviewed-on: https://skia-review.googlesource.com/121000
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/build/gcc b/build/gcc
index 7ba3268..d60d469 100644
--- a/build/gcc
+++ b/build/gcc
@@ -1,5 +1,5 @@
 cc     = gcc
-cflags = -std=c11 -fdiagnostics-color -Wall -Wextra
+cflags = -std=c11 -fdiagnostics-color -Wall -Wextra -fstack-usage
 out    = out/gcc$mode
 
 include build/local