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.
The `needs-asm-support` directive checks whether the host architecture
supports inline assembly, not the target architecture. For tests that
explicitly specify a target via `--target` in their compile-flags, this
directive is incorrect and unnecessary.
These tests are cross-compiling to specific targets (like x86_64, arm,
aarch64, riscv, etc.) that are already known to have stable asm support.
The directive was causing these tests to be incorrectly skipped on hosts
that don't support asm, even though the target does.
Tests with explicit targets should rely on `needs-llvm-components` to
ensure the appropriate backend is available, rather than checking host
asm support.
Improve documentation about `needs-asm-support` directive.
Where supported, VSX is a 64x128b register set which encompasses
both the floating point and vector registers.
In the type tests, xvsqrtdp is used as it is the only two-argument
vsx opcode supported by all targets on llvm. If you need to copy
a vsx register, the preferred way is "xxlor xt, xa, xa".
