libroot/os: Reshuffle stack_trace.cpp a little more.

* Add missing "generic" inclusion on x86; fixes the build there.
* Name the file the same way as the other files in its directory.

Move stack_trace.cpp to generic directory.

4 architectures are using it, so it is generic enough.
Make it error out for platforms where the stack grows in the other
direction. Another implementation can be added for them.

Change-Id: Ia52b5dd34da7b5ebcca0782af079c43d72ba3a8e
Reviewed-on: https://review.haiku-os.org/c/1340
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: add float/double swapping functions.

Change-Id: I07590af796d689b5e97c03a97727edfd58f5a811
Reviewed-on: https://review.haiku-os.org/c/1183
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

glibc: cleanup long double support

- Add 128 bit long double support from current glibc and a few headers
they need
- Move the existing 80 bit float support in a sub directory of generic,
it is not universal to all archs (see file added in docs/develop/arch).
Also include some new .h files for x86 that are needed after these
changes (from newer versions of the glibc).
- Adjust Jamfiles for m68k, x86 and x86_64 to use the 80bit format
- Do not adjust arm jamfiles, it was wrongly using 80bit long double and
should be fixed to use 64bit instead (which means the double functions
can be used with aliases)
- Do not adjust powerpc jamfiles, because it uses yet another format and
we build it without long double support anyways.

Note that I moved only the files that were creating compile errors,
quite likely more of the s_* and e_* files need to be moved to the
specific directories, see glibc list here:

https://sourceware.org/git/?p=glibc.git;a=tree;f=sysdeps/ieee754/ldbl-128
https://sourceware.org/git/?p=glibc.git;a=tree;f=sysdeps/ieee754/ldbl-96

Change-Id: Ic2d8a454ba9a3b99638e4fbb63daf02df0fea403
Reviewed-on: https://review.haiku-os.org/c/1143
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: add defines and minimum set of required files

Gets the stage0 bootstrap to run.
Imlementation is probably nonsense at this point.

Change-Id: I10876efbb54314b864c0ad951152757cdb2fd366
Reviewed-on: https://review.haiku-os.org/c/1061
Reviewed-by: waddlesplash <waddlesplash@gmail.com>