sysutils/shim: unbreak with gcc5 or later

In file included from /usr/local/include/efi/efi.h:35:0,

from shim.c:36:

/usr/local/include/efi/x86_64/efibind.h:88:24: fatal error: stdint.h: No such file or directory

PR: 216707
Reported by: antoine (via exp-run)