Implement <langinfo.h>.

POSIX locale only, as usual.

The GNU YESSTR and NOSTR extensions return the empty string in the C locale,
so I haven't bothered supporting them.

Bug: http://b/1401872
Test: bionic tests
Change-Id: I6846839e4f9f1812344ed5dce0b93f83c0c20eb3
diff --git a/libc/Android.bp b/libc/Android.bp
index f326db3..f0930fe 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1262,6 +1262,7 @@
         "bionic/ifaddrs.cpp",
         "bionic/inotify_init.cpp",
         "bionic/ioctl.cpp",
+        "bionic/langinfo.cpp",
         "bionic/lchown.cpp",
         "bionic/lfs64_support.cpp",
         "bionic/__libc_current_sigrtmax.cpp",