libgcc_s: export integer and floating point __aeabi_ symbols

[mmel]

Summary

Export all integer and floating point __aeabi_ functions defined by
"Run-time ABI for Arm Architecture"  from libgcc, excluding __aeabi_h2f_alt,
__aeabi_f2h_alt and __aeabi_d2h_alt, which are not yet implemented in
compiler-rt.

To maintain ABI backward compatibility, convert __aeabi_ floating-point
symbols previously exported from libc to an explicit non-default version.

Remove guessing of vfp/not-vfp version  for compiler-rt sources. The vfp
version needs additional runtime logic to select the right implementation
and we don't have it implemented.

[andrew]

Will this work with softfloat? If not, and we don't think anyone is using it in 15 then we should remove support for non-VFP HW first.

[mmel]

They are all softfloat - all aeabi functions use softfloat calling convections and compiler-rt implementation doesn't use VFP. I removed the optimized VFP variants from the build (because they needed support in the RT linker). Imho these floating point functions are only used for softfloat binaries and also for Thumb-1 code.

[dim]

Are you planning on MFC'ing this? But LGTM for the rest.

[mmel]

I plan to MFC it, sure. I just forgot to copy all tag lines into the review.