bug#34106: 27.0.50; master build failed with MSYS2/MinGW-w64

[Chris Zheng <chriszheng99@gmail.com>]

When build master branch under MS-Windows I’m seeing this

  CC       pdumper.o
pdumper.c: In function 'dump_cold_bignum':
pdumper.c:3447:53: error: conversion from 'size_t' {aka 'long long unsigned int'} to 'mp_size_t' {aka 'long int'} may change value [-Werror=conversion]
       mp_limb_t limb = mpz_getlimbn (bignum->value, i);
cc1.exe: some warnings being treated as errors

Because with MSYS2/MinGW-w64 the `long' is 32-bit instead of 64-bit.

A explicit cast can fix it.

diff --git a/src/pdumper.c b/src/pdumper.c
index 3787408e6d..9d5ace6c38 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -3444,7 +3444,7 @@ dump_cold_bignum (struct dump_context *ctx, Lisp_Object object)
   Fputhash (object, descriptor, ctx->bignum_data);
   for (size_t i = 0; i < nlimbs; ++i)
     {
-      mp_limb_t limb = mpz_getlimbn (bignum->value, i);
+      mp_limb_t limb = mpz_getlimbn (bignum->value, (mp_size_t) i);
       dump_write (ctx, &limb, sizeof (limb));
     }
 }

Thank you,

Chris