Define FNM_EXTMATCH for musl
Fixes the following compilation errors with musl that does not have FNM_EXTMATCH defined:
| main.c: In function 'expand_matches': | main.c:700:40: error: 'FNM_EXTMATCH' undeclared (first use in this function); did you mean 'FNM_NOMATCH'? | 700 | if(fnmatch(pattern, ifa->ifa_name, FNM_EXTMATCH)) | | ^~~~~~~~~~~~ | | FNM_NOMATCH
and
| archlinux.c:40:28: error: 'FNM_EXTMATCH' undeclared (first use in this function); did you mean 'FNM_NOMATCH'? | 40 | if(fnmatch(pattern, buf, FNM_EXTMATCH) == 0) { | | ^~~~~~~~~~~~ | | FNM_NOMATCH