Update libcurl to version 7.31.0
Compatibility changes for Xcode 5 Command Line Tools

Basically just renaming 'llvm-gcc-4.2' to 'gcc'
Update base SDK and accept arm64 as valid arch

Scripts still can't compile for arm64 but at least now they accept the
architecture as valid :\
Fixes configure for arm64 builds

As arm64 architecture build is now working it is enabled by default.
ios 7.1 64-bit