Optimize code if we have only one personality

On i386:
   text	   data	    bss	    dec	    hex	filename
 238025	    672	  18980	 257677	  3ee8d	strace.before
 237389	    704	  18944	 257037	  3ec0d	strace

* defs.h: Define PERSONALITY0_WORDSIZE as sizeof(long) if not defined.
Introduce new define, current_wordsize as
(personality_wordsize[current_personality]).
Make set_personality() no-op, current_personality constant zero,
current_wordsize as PERSONALITY0_WORDSIZE if we have only one personality.
* count.c (call_summary): Use current_wordsize instead of
personality_wordsize[current_personality].
* desc.c (printflock): Likewise.
* file.c (sys_utime): Likewise.
* io.c (tprint_iov): Likewise.
* process.c (printargv): Likewise.
* resource.c (decode_rlimit): Likewise.
* signal.c (sys_kill): Likewise.
(sys_rt_sigaction): Likewise.
* time.c (sprinttv): Likewise.
(sprint_timespec): Likewise.
(printitv_bitness): Likewise.
(tprint_timex): Likewise.
(printsigevent): Likewise.
* util.c (dumpiov): Likewise.
(umoven): Likewise.
(umovestr): Likewise.
* syscall.c: Initialize sysent to sysent0 etc.
Make current_personality, personality_wordsize[], set_personality()
conditional on SUPPORTED_PERSONALITIES > 1.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/process.c b/process.c
index 2239d4a..7035c2e 100644
--- a/process.c
+++ b/process.c
@@ -858,7 +858,7 @@
 	} cp;
 	const char *sep;
 	int n = 0;
-	unsigned wordsize = personality_wordsize[current_personality];
+	unsigned wordsize = current_wordsize;
 
 	cp.p64 = 1;
 	for (sep = ""; !abbrev(tcp) || n < max_strlen / 2; sep = ", ", ++n) {