This brings i386 and x32 in line with x86_64
and removes redundant HAVE_GETREGS_OLD checks.
Besides that, use of PTRACE_GET_SYSCALL_INFO would require
an extra get_regs() invocation before set_regs().

* syscall.c (ARCH_MIGHT_USE_SET_REGS): Define to 1.
[HAVE_GETREGS_OLD] (ARCH_MIGHT_USE_SET_REGS): Redefine to 0.
(ptrace_setregset_or_setregs): Check ARCH_MIGHT_USE_SET_REGS instead
of HAVE_GETREGS_OLD.
* linux/i386/arch_regs.c (ARCH_MIGHT_USE_SET_REGS): Redefine to 0.
* linux/powerpc/arch_regs.c: Likewise.
* linux/x86_64/arch_regs.c: Likewise.
* linux/i386/set_error.c (arch_set_error, arch_set_success)
[!HAVE_GETREGS_OLD]: Remove.
* linux/i386/set_scno.c (arch_set_scno) [!HAVE_GETREGS_OLD]: Remove.
* linux/powerpc/set_error.c (arch_set_error, arch_set_success)
[!HAVE_GETREGS_OLD]: Remove.
* linux/powerpc/set_scno.c (arch_set_scno) [!HAVE_GETREGS_OLD]: Remove.
* linux/x86_64/set_error.c [!HAVE_GETREGS_OLD]: Remove.
* linux/x86_64/set_scno.c: Likewise.