Fix dwarf2 unwinding through futex functions.

When profiling programs with lock problems with perf record -g dwarf,
libunwind can currently not backtrace through the futex and unlock
functions in pthread. This is because they use out of line sections,
and those are not correctly described in dwarf2 (I believe needs
dwarf3 or 4).

This patch first removes the out of line sections. They only save a
single jump, but cause a lot of pain. Then it converts the now inline
lock code to use the now standard gas .cfi_* commands.

With these changes libunwind/perf can backtrace through the futex
functions now.

Longer term it would be likely better to just use C futex() functions
on x86 like all the other architectures. This would clean the code up
even more.