Mark functions not returning as sudo_noreturn

We also put NOTREACHED where it applies.

plugins/sudoers/regress/check_symbols/check_symbols.c

@@ -31,7 +31,7 @@
 
 sudo_dso_public int main(int argc, char *argv[]);
 
-static void
+sudo_noreturn static void
 usage(void)
 {
     fprintf(stderr, "usage: %s plugin.so symbols_file\n", getprogname());

plugins/sudoers/regress/iolog_plugin/check_iolog_plugin.c

@@ -44,7 +44,7 @@ struct sudo_plugin_event * (*plugin_event_alloc)(void);
 
 sudo_dso_public int main(int argc, char *argv[], char *envp[]);
 
-static void
+sudo_noreturn static void
 usage(void)
 {
     fprintf(stderr, "usage: %s pathname\n", getprogname());

plugins/sudoers/regress/parser/check_addr.c

@@ -65,7 +65,7 @@ check_addr(char *input)
     return 0;
 }
 
-static void
+sudo_noreturn static void
 usage(void)
 {
     fprintf(stderr, "usage: %s datafile\n", getprogname());