Use MANGLE in cavsdsp.c to save two registers using gcc.

Fixes compilation with !HAVE_6REGS.
Fix compilation with !HAVE_6REGS.

Can be tested with:
$ ./configure --cc='cc -m32' --disable-optimizations --enable-pic
configure: Handle armcc 5.0

The first line of the "armcc --vsn" output in one version is
"Product: ARM Compiler 5.04".

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit '4936ef6492f640e1606c6507f2c4e495164d3974'

* commit '4936ef6492f640e1606c6507f2c4e495164d3974':
  configure: Handle armcc 5.0

Conflicts:
	configure

See: db55365d0f938ee93ed660a14c07f10f2a66dd10
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'cehoyos/master'

* cehoyos/master:
  Fix compilation with !HAVE_6REGS.
  Use MANGLE in cavsdsp.c to save two registers using gcc.

Merged-by: Michael Niedermayer <michaelni@gmx.at>