Deduplicating __NR_* and SYS_* syscall defines

[Bobby Bingham <koorogi@koorogi.info>]

During the powerpc64 review, Rich mentioned wanting to replace the
arch/*/bits/syscall.h files with .in files that would be preprocessed with
something like:

    sed -e p -e s/__NR_/SYS_/ < $< > $@

This would eliminate a lot of intra-file duplication here.

I took a look, and this won't quite work as-is, because the following
lines in the arm version would end up outputting duplicate definitions:

    #define __ARM_NR_breakpoint	0x0f0001
    #define __ARM_NR_cacheflush	0x0f0002
    #define __ARM_NR_usr26		0x0f0003
    #define __ARM_NR_usr32		0x0f0004
    #define __ARM_NR_set_tls	0x0f0005

Same thing for this line in x32:

    #define __X32_SYSCALL_BIT        0x40000000

I'm thinking something like the following awk script would work:

    {
        print
    }

    $1 ~ /^#(define|undef)$/ && $2 ~ /^__NR_/ {
        sub(/__NR_/, "SYS_", $2)
        print
    }

The handling for #undef is for the x32 file.  It looks like only the
`#undef __NR_getdents' in that file is actually necessary, and even that
could be avoided by just omitting the earlier line:

    #define __NR_getdents (__X32_SYSCALL_BIT + 78)

So maybe we can get rid of the #undefs there, and simplify the awk script
accordingly.

Thoughts on this approach?  If this sounds ok, I'll submit a patch.

--
Bobby