use global_asm! / support more platforms / use cross to test

[LaoLittle]

• use global_asm! instead of external toolchain
• add armv7/riscv64 Linux support
• README: add Android
• use cross in ci to test on multiple platforms
• use sysv64 abi on windows

[LaoLittle]

macOS aarch64 tested loongarch64 is not tested

the rest can be found in ci

[Xudong-Huang]

Thanks for the big change!