Package global fails to compile on MacOS 11.1

[Michael Labbé]

Package global failed to compile on my arm 11.1 system. This is due to an error 
because realpath cannot be found. The fix is to modify configure to include 
stdlib.h.

Line 14291 of configure on global-6.6.5:

main(){ (void)realpath("/./tmp", (void *)0); return 0; }
Insert one line before that:

#include<stdlib.h>
main(){ (void)realpath("/./tmp", (void *)0); return 0; }
configure now succeeds.