minor change to default compile flags

Modules/Platform/gcc.cmake

@@ -1,10 +1,10 @@
 SET (CMAKE_CXX_FLAGS_INIT "")
 SET (CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-SET (CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-O3")
-SET (CMAKE_CXX_FLAGS_RELEASE_INIT "-O2")
+SET (CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-Os")
+SET (CMAKE_CXX_FLAGS_RELEASE_INIT "-O3")
 SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
 SET (CMAKE_C_FLAGS_INIT "")
 SET (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-SET (CMAKE_C_FLAGS_MINSIZEREL_INIT "-O3")
-SET (CMAKE_C_FLAGS_RELEASE_INIT "-O2")
+SET (CMAKE_C_FLAGS_MINSIZEREL_INIT "-Os")
+SET (CMAKE_C_FLAGS_RELEASE_INIT "-O3")
 SET (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")