Add release flags to iOS toolchain.

- Without explicitly specifying the flags for release compilation in
  the iOS toolchain file, no additional flags are passed and so the
  libraries were not being built with full optimisations, even though
  the CMAKE_BUILD_TYPE was 'Release'.

Change-Id: I742bab7589906b556640776d481491a8cc2303d4

cmake/iOS.cmake

diff --git a/cmake/iOS.cmake b/cmake/iOS.cmake
index 5ad71ad..03b845a 100644
--- a/cmake/iOS.cmake
+++ b/cmake/iOS.cmake
@@ -110,6 +110,7 @@
 # Hidden visibilty is required for cxx on iOS
 set (CMAKE_C_FLAGS_INIT "")
 set (CMAKE_CXX_FLAGS_INIT "-fvisibility=hidden -fvisibility-inlines-hidden")
+set (CMAKE_CXX_FLAGS_RELEASE_INIT "-DNDEBUG -O3 -fomit-frame-pointer -ffast-math")
 
 set (CMAKE_C_LINK_FLAGS "-Wl,-search_paths_first ${CMAKE_C_LINK_FLAGS}")
 set (CMAKE_CXX_LINK_FLAGS "-Wl,-search_paths_first ${CMAKE_CXX_LINK_FLAGS}")