Revert "Unregister pthread_atfork handlers on dlclose()"

 The visibility control in pthread_atfork.h is incorrect.
 It breaks 64bit libc.so by hiding pthread_atfork.

 This reverts commit 6df122f8528f9b9fcf7dfea14ae98b0ef66274e1.

Change-Id: I21e4b344d500c6f6de0ccb7420b916c4e233dd34
diff --git a/libc/Android.mk b/libc/Android.mk
index 8ed969f..4a199e7 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -63,7 +63,6 @@
     stdio/sprintf.c \
     stdio/stdio.c \
     stdio/stdio_ext.cpp \
-    stdlib/atexit.c \
     stdlib/exit.c \
 
 # Fortify implementations of libc functions.
@@ -482,6 +481,7 @@
     upstream-openbsd/lib/libc/stdio/wprintf.c \
     upstream-openbsd/lib/libc/stdio/wscanf.c \
     upstream-openbsd/lib/libc/stdio/wsetup.c \
+    upstream-openbsd/lib/libc/stdlib/atexit.c \
     upstream-openbsd/lib/libc/stdlib/atoi.c \
     upstream-openbsd/lib/libc/stdlib/atol.c \
     upstream-openbsd/lib/libc/stdlib/atoll.c \