ape does use _brk, so put it in the various (still duplicated, sorry) headers
instead of defining it on the fly.  sbrk should also move to the header file,
but that would require some more re-orginization.

Reference: /n/atom/patch/applied2013/ape_brk
Date: Thu Jul 11 17:23:43 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/ape/lib/9/libc.h	Thu Jul 11 17:22:35 2013
+++ /sys/src/ape/lib/9/libc.h	Thu Jul 11 17:22:35 2013
@@ -70,6 +70,7 @@
 extern	int	_AWAIT(char*, int);
 extern	int	_ALARM(unsigned long);
 extern	int	_BIND(const char*, const char*, int);
+extern	int	_BRK_(void*);
 extern	int	_CHDIR(const char*);
 extern	int	_CLOSE(int);
 extern	int	_CREATE(char*, int, unsigned long);
--- /sys/src/ape/lib/ap/plan9/brk.c	Thu Jul 11 17:22:35 2013
+++ /sys/src/ape/lib/ap/plan9/brk.c	Thu Jul 11 17:22:35 2013
@@ -5,7 +5,6 @@
 
 char	end[];
 static	char	*bloc = { end };
-extern	int	_BRK_(void*);
 
 enum
 {
--- /sys/src/ape/lib/ap/plan9/sys9.h	Thu Jul 11 17:22:35 2013
+++ /sys/src/ape/lib/ap/plan9/sys9.h	Thu Jul 11 17:22:35 2013
@@ -77,6 +77,7 @@
 extern	int	_AWAIT(char*, int);
 extern	int	_ALARM(unsigned long);
 extern	int	_BIND(const char*, const char*, int);
+extern	int	_BRK_(void*);
 extern	int	_CHDIR(const char*);
 extern	int	_CLOSE(int);
 extern	int	_CREATE(char*, int, unsigned long);