ARM: vp56: allow inline asm to build with clang

ARM: vp56: allow inline asm to build with clang

The clang integrated assembler does not support pre-UAL syntax,
while gcc requires pre-UAL syntax for ARM code.  A patch[1] for
clang to support the old syntax as well has been ignored since
January.

This patch chooses the syntax appropriate for each compiler,
allowing both to build the code.  Notably, this change allows
building for iphone with the latest Apple Xcode update.

[1] http://llvm.org/bugs/show_bug.cgi?id=11855

Signed-off-by: Mans Rullgard <mans@mansr.com>