hardlink, wall: fix variable shadowing

hardlink, wall: fix variable shadowing

misc-utils/hardlink.c:91:65: warning: declaration shadows a variable in the global scope [-Wshadow]
misc-utils/hardlink.c:73:5: note: previous declaration is here
int content_only = 0;

term-utils/wall.c:114:40: warning: declaration shadows a variable in the global scope [-Wshadow]
term-utils/wall.c:129:65: warning: declaration shadows a variable in the global scope [-Wshadow]
/usr/include/bits/getopt_core.h:36:14: note: previous declaration is here
extern char *optarg;

Signed-off-by: Sami Kerola <kerolasa@iki.fi>