Add support for mul[s/d]f3vfp and div[s/d]f3vfp

[paoloteti]

Here using "C" the compiler will use "aapcs" or "aapcs-vfp" depending on target configuration.

Of course this translates in a call to __aeabi_fdiv / __aeabi_fmul on non-HF targets.

On eabi targets with +vfpv2/vfpv3 LLVM generate:

   vmov	s0, r1
   vmov	s2, r0
   vdiv.f32	s0, s2, s0
   vmov	r0, s0
   bx	lr

On eabihf targets with +vfpv3-d16/d32/f32 +fp-only-sp LLVM generate:

  vdiv.f32	s0, s0, s1
  bx	lr

That's exactly what We need for [div/mul][s/d]f3vfp.S

[alexcrichton]

Thanks! Could you be sure to add some tests for these as well?

[paoloteti]

Done! Of course on QEMU/TravisCI We still have an ICE:

error: internal compiler error: librustc_metadata/cstore_impl.rs:131: get_optimized_mir: missing MIR for DefId(3/0:10 ~ utest_cortex_m_qemu[f0f1]::lang_items[0]::start[0])

[alexcrichton]

Thanks! Ah yeah it's fine to ignore the thumb targets on CI (feel free to add an allow_failure if you're enterprising!) but looks like other targets may be failing as well?

[alexcrichton]

Thanks!