Build mapnik for ios, including arm64

Updated the rebuild_ios.sh script to build a universal i386/armv7/armv7s/arm64 lib.
Run ./scripts/rebuild_ios.sh from ./osx folder

It seems to build fine (it's usable without any issues so far) but the script currently fails at the last step:
./scripts/package_mobile_sdk.sh: line 67: ./dist/bin/bcp: No such file or directory
The comment, "required for bcp header copy", in the rebuild_ios.sh script hint that building the x86_64 arch is required for the packaging to succeed, but it failed the same way regardless. I've commented out the x86 from the script since it's not needed when targeting ios.

Afterwards I needed to manually copy the mapnik includes from the source into the out-directory.
Probably as a result of the packaging step not succeeding..?