flac: Implement --no-error-on-compression-fail command line option.

This is designed for the test suite where a number of artificially created
files end up bigger than the original.
test/ : Use new --no-error-on-compression-fail option as needed.
Split regain play tests into separate script.
stream_encoder.c : Improve fix for arithmetic overflow.

Only use the 32 bit accumulator if the input data is 16 bits or less.
test/test_replaygain.sh : Prefer mawk over gawk.

The AWK script used to generate tones for this test fails with gawk
version 4.0.1, but used to work for earlier versions. Use mawk instead
if it exists.
configure.ac : Improve asm optimisation detection.

When compiling for ia32 on an x86_64 kernel, the configure script
was not detecting the ability to do asm optimisations because the
configure script was detecting the x86_64 kernel not the ia32
user space.
src/libFLAC/ia32/nasm.h : Fix nasm warning on windows.

Patch from Ozkan Sezer <sezeroz@gmail.com>.
Fix a couple of NASM warnings.

Suggested by Ozkan Sezer <sezeroz@gmail.com>.