Optimize Declarator to avoid malloc/free traffic for the argument list of a

function DeclaratorChunk in common cases.  This uses a fixed array in 
Declarator when it is small enough for the first function declarator chunk
in a declarator.

This eliminates all malloc/free traffic from DeclaratorChunk::getFunction
when running on Cocoa.h except for five functions: signal/bsd_signal/sigset,
which have multiple Function DeclChunk's, and 
CFUUIDCreateWithBytes/CFUUIDGetConstantUUIDWithBytes, which take more than
16 arguments.

This patch was pair programmed with Steve.

llvm-svn: 62599