build for android 16k pagesize by default, update android api 21 (Ten…

…cent#5833)

w

define empty assertion termination function for fixing linking with o…

…ld android ndk

fix clang avx512bf16 build (Tencent#5842)

* check compiler supports isa with optimization enabled

Update README.md

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fix

set MACOSX_DEPLOYMENT_TARGET

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