crunchgen: fix MK_AUTO_OBJ logic after r364166

r364166 converted echo -n `/bin/pwd` to a raw pwd invocation, leaving a
trailing newline at the end of path.  This caused a later stat() of it to
erroneously fail and the fallback to MK_AUTO_OBJ=no logic proceeded as
unexpected.

Harry Schmalzbauer bissected the resulting build failure he experienced
(stable/12 host, -HEAD build) down to r365887. This change is mostly
unrelated, except it switches the build to bootstrapped crunchgen - clue!

I then bissected recent crunchgen changes going back a bit since we wouldn't
observe the failure immediately with -CURRENT in most configurations, which
landed me on r364166. After many intense head-scratching minutes and printf
debugging, I realized that the newline was the difference. This is where our
tale ends.

Reported by:	Harry Schmalzbauer, O. Hartmann, Mike Tancsa, kevans
MFC after:	3 days

usr.sbin/crunch/crunchgen/crunchgen.c

@@ -666,6 +666,8 @@ fillin_program(prog_t *p)
 		if (!*path)
 			errx(1, "Can't perform pwd on: %s\n", p->srcdir);
 
+		/* Chop off trailing newline. */
+		path[strlen(path) - 1] = '\0';
 		p->realsrcdir = strdup(path);
 	}