Optmize bitmapword macros calc (src/backend/nodes/bitmapset.c)

Hi,

IMO I believe that bitmapset can obtain an optimization in the calculation
of the WORDNUM and BITNUM macros.

As you know, in bitmapset, negative members are not allowed.

if (x < 0)
elog(ERROR, "negative bitmapset member not allowed");

Then, allow the compiler to optimize and do the calculations in unsigned.

I did a demonstration in compiler explorer.
https://godbolt.org/z/c68o43Eq1

It is demonstrated here as well.

#define WORDNUM_f1(x) ((x) / BITS_PER_BITMAPWORD)
         mov eax, DWORD PTR [rbp-20]
         lea edx, [rax+63]
         test eax, eax
         cmovs eax, edx
         sar eax, 6
         mov DWORD PTR [rbp-4], eax

#define WORDNUM_f2(x) ((bitmapword) (x) / BITS_PER_BITMAPWORD)
         mov eax, DWORD PTR [rbp-20]
         cdqe
         shr rax, 6
         mov DWORD PTR [rbp-4], eax


#define BITNUM_f1(x) ((x) % BITS_PER_BITMAPWORD)
         mov edx, DWORD PTR [rbp-20]
         mov eax, edx
         sar eax, 31
         shr eax, 26
         add edx, eax
         and edx, 63
         sub edx, eax
         mov DWORD PTR [rbp-4], edx

#define BITNUM_f2(x) ((bitmapword) (x) % BITS_PER_BITMAPWORD)
        mov eax, DWORD PTR [rbp-20]
         and eax, 63
         mov DWORD PTR [rbp-4], eax