configure: Allow command-line configure for ppc32

Similar to manually selecting i386 for an x86_64 host.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-ppc: Avoid code for nop move

While these are rare from code that's been through the optimizer,
it's not uncommon within the tcg backend.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-ppc: Cleanup tcg_out_qemu_ld/st_slow_path

Coding style fixes.  Use TCGReg enumeration values instead of raw
numbers.  Don't needlessly pull the whole TCGLabelQemuLdst struct
into local variables.  Less conditional compilation.

No functional changes.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-ppc: Use conditional branch and link to slow path

Saves one insn per slow path.  Note that we can no longer use
a tail call into the store helper.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-ppc: Fix and cleanup tcg_out_tlb_check

The fix is that sparc has so many mmu modes that the last one overflowed
the 16-bit signed offset we assumed would fit.  Handle this, and check
the new assumption at compile time.

Load the tlb addend earlier for the fast path.

Remove the explicit address + addend and make use of index addressing.

Adjust constraints for qemu_ld64 such that we don't clobber the address
register or tlb addend before loading both values.

Signed-off-by: Richard Henderson <rth@twiddle.net>