mail/hashcash: fix build on powerpc*

• fastmint_library.o ---

fastmint_library.c: In function 'minter_library':
fastmint_library.c:92:17: error: implicit declaration of function 'SHA1_Transform'; did you mean 'SHA1_Xform'? [-Wimplicit-function-declaration]

92 |                 SHA1_Transform( H, X );
   |                 ^~~~~~~~~~~~~~
   |                 SHA1_Xform