Compile ASM failed.

[winlinvip]

When we use setjmp/longjmp in glibc, we still compile the md.S, which fail in some OS.

We support a macro to disable the md.S MD_ST_NO_ASM, you can enable it to avoid building md.S:

1. Directly build ST: make EXTRA_CFLAGS=-DMD_ST_NO_ASM
2. Build SRS with ST: ./configure --extra-flags='-DMD_ST_NO_ASM' && make