dir.c: rename str(n)cmp_icase to fspath(n)cmp

These functions compare two paths that are taken from file system.
Depending on the running file system, paths may need to be compared
case-sensitively or not, and maybe even something else in future. The
current names do not convey that well.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -301,7 +301,7 @@ static int link_alt_odb_entry(const char *entry, const char *relative_base,
 			return -1;
 		}
 	}
-	if (!strcmp_icase(ent->base, normalized_objdir)) {
+	if (!fspathcmp(ent->base, normalized_objdir)) {
 		free(ent);
 		return -1;
 	}