1¡¢About builtin_tls
  Q1: What if the size of the tls used by libc is larger than the builtin size?
      https://github.com/bminor/musl/blob/master/ldso/dynlink.c#L1785


  Q2: I haven¡¯t seen any processing of the tls segment of ldso, so how does __copy_tls take effect at this time£¬ where was  libc.tls_head be modified before this time?
      https://github.com/bminor/musl/blob/master/src/env/__init_tls.c#L64


  Q3: Is it possible to init main thread tls by calling malloc according to the tls size of libc at this time?


2¡¢About libc and other so use tls at the same time
	I didn¡¯t see musl modify tls_offset when ldso uses tls, so when another so uses tls later, their tls offsets will conflict.