Operand of asm("call") (the callee function) is represented

as "X" constraint and "P" modifier on x86.  Make this work.
(Change may not be sufficient to fix it for non-Darwin, but
I'm pretty sure it won't break anything.)
gcc.apple/asm-block-32.c
gcc.apple/asm-block-33.c

llvm-svn: 74967