Synchronize sysdep.h with current glibc

So that I can more easily import sparc headers from it.

NO_UNDERSCORES is gone and is now always the default.
Some previously arch-specific defines are now valid for all platforms.

Change-Id: If9876b241719559bdcb5cd9d8b1dc97e5e3d96b3
Reviewed-on: https://review.haiku-os.org/c/1141
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

Added x86_64 math functions to libroot.

These have been pulled from glibc 2.10, the last version before a
bunch of changes were made that would have made porting more difficult.
None of this has been tested yet, it is not currently possible to do
so: I'm just trying to get libroot compiling so that I can work on the
runtime loader. I will test them when I am able to.

Added x86_64 math functions to libroot.

These have been pulled from glibc 2.10, the last version before a
bunch of changes were made that would have made porting more difficult.
None of this has been tested yet, it is not currently possible to do
so: I'm just trying to get libroot compiling so that I can work on the
runtime loader. I will test them when I am able to.