Make gas parse '__tls_get_addr(foo@tlsgd)'.

Corresponds to 727fc41e077139570ea8b8ddfd6c546b2a55627c.

This allows us to use -no-integrated-as with clang, if we prefer.

Obtained from:	binutils-gdb (Relicensed from Alan Modra as GPLv2)
MFC after:	2 weeks
X-MFC-with:	r275718