[ObjC] Disallow vector parameters and return values in Objective-C methods

for iOS < 9 and OS X < 10.11 X86 targets

This commit adds a new error that disallows methods that have parameters/return
values with a vector type for some older X86 targets. This diagnostic is
needed because objc_msgSend doesn't support SIMD vector registers/return values
on X86 in iOS < 9 and OS X < 10.11. Note that we don't necessarily know if the
vector argument/return value will use a SIMD register, so instead we chose to
be conservative and prohibit all vector types.

rdar://21662309

Differential Revision: https://reviews.llvm.org/D28670

llvm-svn: 301532