unused macro MPN_PTR_SWAP in mini-gmp.c

[Paul Eggert]

In libgmp 6.2.1, mini-gmp.c defines a macro without using it, causing 
the command "gcc -Wunused-macros -Werror" to fail with the following 
diagnostic:

lib/mini-gmp.c:251: warning: macro "MPN_PTR_SWAP" is not used 
[-Wunused-macros]
   251 | #define MPN_PTR_SWAP(xp,xs, yp,ys) 
         \
       |

Proposed patch attached.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: gmp.patch
Type: text/x-patch
Size: 486 bytes
Desc: not available
URL: <https://gmplib.org/list-archives/gmp-bugs/attachments/20220308/bd8063bb/attachment.bin>