add ARM64 Adaptative Quantization code and UT
Consistently use -f elf instead of -f elf32

The freebsd platform file already did things like this.
Mark the x86 assembly object files as not requiring an executable stack

This avoids having to add extra linker flags in order to specify this.

This is similar to how this already is handled for the arm assembly.
Merge pull request #1203 from dongzha/AddAQArm64

add ARM64 Adaptative Quantization code and UT
Merge pull request #1215 from mstorsjo/x86-asm-noexec-stack

Mark the x86 assembly object files as not requiring an executable stack
    add encoder interface ut
Merge pull request #1220 from ruil2/interface_ut

    add encoder interface ut
Merge remote-tracking branch 'upstream/master' into travis.osx