Increase the mamake buffer size to 4096 (#97)

src/cmd/INIT/mamake.c:
- Fix a rare build error by applying Oracle's patch to increase
  mamake's buffer size[*]. Description from the original patch:

  The build of KornShell might spuriously fail
  with the following error.
  ...
  /usr/bin/ksh: line 40: syntax error at line 44: `else unmatched
  mamake [lib/libast]: *** exit code 3 making ast.req
  mamake: *** exit code 139 making lib/libast

  The patch increases the buffer size of mamake to avoid
  spurious build failures.

  I can't reproduce build error, but this patch should be merged
  anyway because OpenSUSE also increases mamake's buffer size
  in a patch titled 'workaround-stupid-build-system.diff'[**].
  This indicates that the build failure is a heisenbug that can
  occur on at least Linux and Solaris.

  [*]: oracle/solaris-userland@7cad9da
  [**]: https://build.opensuse.org/package/view_file/shells/ksh/workaround-stupid-build-system.diff?expand=1

src/cmd/INIT/mamake.c

@@ -118,7 +118,7 @@ USAGE_LICENSE
 #define set(b,o)	((b)->nxt=(b)->buf+(o))
 #define use(b)		(*(b)->nxt=0,(b)->nxt=(b)->buf)
 
-#define CHUNK		1024
+#define CHUNK		4096
 #define KEY(a,b,c,d)	((((unsigned long)(a))<<15)|(((unsigned long)(b))<<10)|(((unsigned long)(c))<<5)|(((unsigned long)(d))))
 #define NOW		((unsigned long)time((time_t*)0))
 #define ROTATE(p,l,r,t)	((t)=(p)->l,(p)->l=(t)->r,(t)->r=(p),(p)=(t))