mpg123: add textrel to INSANE_SKIP

The x86 assembler optimisations contains text relocations and there
are no upstream plans to fix them:

  http://sourceforge.net/p/mpg123/bugs/168/



Benchmarking suggests that the SSE assembler is still clearly faster
than the generic C code, so leave the assembler optimisations enabled.

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>