libroot: Add brk() and sbrk().

This commit replaces the placeholder implementation of sbrk(), which
operated on a process' heap, with real implementations of brk() and
sbrk() that adjust a process' program break.

* unistd.h: Add standard definitions of brk() and sbrk(); include
  stdint.h for intptr_t.
* thread.cpp: Recognize RLIMIT_AS and RLIMIT_DATA resource limits
  (both currently unlimited); order limit identifiers alphabetically.
* arch-specific.cpp: Remove sbrk_hook().
* malloc_debug_api.cpp: Remove sbrk_hook().
* unistd/Jamfile: Build brk.c instead of sbrk.c.
* unistd/brk.c: Add.
* unistd/sbrk.c: Delete (placeholder implementation).
* libroot_stubs.c: Remove sbrk_hook().
* libroot_stubs_legacy.c: Remove sbrk_hook().
* src/tests/.../posix/Jamfile: Build brk_test.c.
* brk_test.c: Add (simple unit test that demonstrates behaviour of
  sbrk()).

Signed-off-by: Jérôme Duval <[email protected]>

headers/posix/unistd.h

@@ -7,6 +7,7 @@
 
 
 #include <null.h>
+#include <stdint.h>
 #include <sys/types.h>
 
 
@@ -221,7 +222,9 @@ extern void		_exit(int status) __attribute__ ((noreturn));
 
 extern pid_t	tcgetpgrp(int fd);
 extern int		tcsetpgrp(int fd, pid_t pgrpid);
-extern void		*sbrk(long incr);
+
+extern int		brk(void *addr);
+extern void		*sbrk(intptr_t increment);
 
 extern unsigned	int	alarm(unsigned int seconds);
 extern useconds_t	ualarm(useconds_t microSeconds, useconds_t interval);