libc: introduce "jehanne_" namespace

With this commit all functions declared in libc.h have been renamed
with the "jehanne_" prefix. This is done for several reason:

- it removes conflicts during symbol resolution when linking
  standard C libraries like newlib or musl
- it allows programs depending on a standard C library to directly
  link to a library depending on our non standard libc (eg libsec).

To ease transiction two files are provided:

- sys/include/lib9.h that can be included instead of <libc.h> to use
  the old names (via a simple set of macros)
- sys/src/lib/c/lib9.c that can be compiled with a program where the
  macro provided by lib9.h are too dumb (see for example rc or grep).

In the kernel port/lib.h has been modified accordingly and some of
the functions it directly provides has been renamed too (eg malloc
in qmalloc.c and print in devcons.c).

sys/include/ip.h

@@ -192,8 +192,8 @@ uint16_t	ptclbsum(uint8_t*, int);
 int	v6tov4(uint8_t*, uint8_t*);
 void	v4tov6(uint8_t*, uint8_t*);
 
-#define	ipcmp(x, y) memcmp(x, y, IPaddrlen)
-#define	ipmove(x, y) memmove(x, y, IPaddrlen)
+#define	ipcmp(x, y) jehanne_memcmp(x, y, IPaddrlen)
+#define	ipmove(x, y) jehanne_memmove(x, y, IPaddrlen)
 
 extern uint8_t IPv4bcast[IPaddrlen];
 extern uint8_t IPv4bcastobs[IPaddrlen];