libbb: make trim() return pointer to terminating NUL

function                                             old     new   delta
trim                                                  80      90     +10
angle_address                                         56      50      -6
sysctl_main                                          282     273      -9
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/3 up/down: +10/-15)           Total:  -5 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/trim.c

@@ -10,9 +10,10 @@
 
 #include "libbb.h"
 
-void FAST_FUNC trim(char *s)
+char* FAST_FUNC trim(char *s)
 {
 	size_t len = strlen(s);
+	size_t old = len;
 
 	/* trim trailing whitespace */
 	while (len && isspace(s[len-1]))
@@ -26,5 +27,12 @@ void FAST_FUNC trim(char *s)
 			memmove(s, nws, len);
 		}
 	}
-	s[len] = '\0';
+
+	s += len;
+	/* If it was a "const char*" which does not need trimming,
+	 * avoid superfluous store */
+	if (old != len)
+		*s = '\0';
+
+	return s;
 }