implemented a (codegen) target hook for __builtin_extend_pointer.
I'm also making it return a uint64_t instead of an unsigned word; this
comports with typical usage (i.e. the one use I know of).
I don't know if any of the existing targets requires this hook to be
set (other than x86 and x86_64, which I know do not).
llvm-svn: 97547
1. Add helper class for sema checks for target attributes
2. Add helper class for codegen of target attributes
As a proof-of-concept - implement msp430's 'interrupt' attribute.
llvm-svn: 93118
John McCall