Rollup merge of #149679 - pmur:murp/ppc-inline-improvements, r=Amanieu

Restrict spe_acc to PowerPC SPE targets

Update the tests, add powerpc-*-gnuspe testing, and create a distinct clobber_abi list for PowerPC SPE targets.

Note, the SPE target does not have vector, vector-scalar, or floating-point specific registers.

r? ```@Amanieu```

Author: matthiaskrgr