Remove some problematic APIs

In order to improve our chances of success building other open source
projects we shouldn't define APIs that'll lead any ./configure script
astray. For example:

- brk() and sbrk() can break mac/windows support
- syscall() is a superb way to break portability
- arch_prctl() is the greatest of all horror shows

third_party/make/main.c

@@ -636,13 +636,11 @@ expand_command_line_file (const char *name)
 
 /* Toggle -d on receipt of SIGUSR1.  */
 
-#ifdef SIGUSR1
 static RETSIGTYPE
 debug_signal_handler (int sig UNUSED)
 {
   db_level = db_level ? DB_NONE : DB_BASIC;
 }
-#endif
 
 static void
 decode_debug_flags (void)
@@ -1609,9 +1607,7 @@ main (int argc, char **argv, char **envp)
 #endif
 
   /* Let the user send us SIGUSR1 to toggle the -d flag during the run.  */
-#ifdef SIGUSR1
   bsd_signal (SIGUSR1, debug_signal_handler);
-#endif
 
   /* Define the initial list of suffixes for old-style rules.  */
   set_default_suffixes ();