Use CCASFLAGS when assembling .S sources

This allows overriding whether all of CFLAGS should be passed
when assembling.
Don't pass all MSVC specific cflags to gas-preprocessor and armasm

This avoids having to disambiguate between assembler parameters,
preprocessor parameters and MSVC parameters within gas-preprocessor.

In particular, this avoids creating a stray dependency file named
'-.d' while building. Future versions of gas-preprocessor might
require this in order to build at all.
clean redundant code
Merge pull request #840 from ganyangbbl/clear_code

clean redundant code
Merge pull request #832 from mstorsjo/asflags

Don't pass all MSVC specific cflags to gas-preprocessor and armasm
modify bs buffer size to double the AU size
Remove unnecessary writing of nal length in the decoder

The written nal length doesn't seem to be used at all.
Merge pull request #847 from mstorsjo/remove-write-nal-length

Remove unnecessary writing of nal length in the decoder
Merge pull request #845 from huili2/bs_buffer_modif

modify bs buffer size to double the AU size at decoder
add minimum buffer size
Merge pull request #854 from sijchen/bufferlencheck_fix

It is OK for this bug
update branch name in build scrpts
Merge branch 'master' of https://github.com/cisco/openh264 into perf-test
modify makefile as library name changed