make pidfile writing configurable.
[ui]toa_to_buf: change API. No users yet.
diff --git a/libbb/Kbuild b/libbb/Kbuild
index ffded6a..a3b78ef 100644
--- a/libbb/Kbuild
+++ b/libbb/Kbuild
@@ -61,6 +61,7 @@
 lib-y += perror_msg_and_die.o
 lib-y += perror_nomsg.o
 lib-y += perror_nomsg_and_die.o
+lib-y += pidfile.o
 lib-y += process_escape_sequence.o
 lib-y += procps.o
 lib-y += read.o