Make a brk/sbrk emulation.

Mac OS X seems to have some difficulties with brk/sbrk (maybe with the
4MB heap limit), and replace all the allocation logic will be prone to
errors, I'll add a new define and lib to emulate brk/sbrk using more
standard allocation methods. By default the heap is 64MB, it should be
enough.

util/LLgen/pmfile-ack

@@ -26,6 +26,8 @@ tool_LLgen = cprogram {
 	cfile (d.."src/Lpars.c"),
 	cfile (d.."src/tokens.c"),
 
+	lib_sbrk,
+
 	outputs = {"%U%/LLgen"},
 	install = pm.install("%TOOLDIR%LLgen")
 }