introduce bb_putchar(). saves ~1800 on uclibc (less on glibc).

diff --git a/miscutils/ttysize.c b/miscutils/ttysize.c
index 5a3f5dc..292cfb8 100644
--- a/miscutils/ttysize.c
+++ b/miscutils/ttysize.c
@@ -39,6 +39,6 @@
 			fmt = "%u %u" + 2; /* " %u" */
 		}
 	}
-	putchar('\n');
+	bb_putchar('\n');
 	return 0;
 }