Macos build problem: missing lgamma_r

With macos and gnumeric-1.12.45 we're getting:

  CC       libspreadsheet_la-sf-gamma.lo
sf-gamma.c:616:10: error: implicit declaration of function 'lgamma_r' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        res_a = gnm_lgamma_r (a, &sign_a);
                ^
./numbers.h:187:22: note: expanded from macro 'gnm_lgamma_r'
#define gnm_lgamma_r lgamma_r
                     ^