Optimize for size.

Change-Id: I7013a57ab7d6bc1916d0a87b72ae826409a34ee9
Reviewed-on: https://swiftshader-review.googlesource.com/4442
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2745f0e..0d0c16d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -148,9 +148,9 @@
     set_cpp_flag("-s" RELEASE)
 
     # For distribution it is more important to be slim than super optimized
-    # so even in Release we us only -O2
-    set_cpp_flag("-O2" RELEASE)
-    set_cpp_flag("-O2" RELWITHDEBINFO)
+    # so even in Release we use only -O2
+    set_cpp_flag("-O2 -Os" RELEASE)
+    set_cpp_flag("-O2 -Os" RELWITHDEBINFO)
 
     set_cpp_flag("-DNDEBUG" RELEASE)
     set_cpp_flag("-DNDEBUG" RELWITHDEBINFO)