Implement <iconv.h>.

Bug: http://b/32978596
Test: ran tests
Change-Id: I56b6ae3d9c5a3a56d2b4afba33fb8f9e964bf7b9
diff --git a/libc/libc.arm.map b/libc/libc.arm.map
index 6ababa1..fe14018 100644
--- a/libc/libc.arm.map
+++ b/libc/libc.arm.map
@@ -1323,6 +1323,9 @@
     __freading; # future
     __fwriting; # future
     getlogin_r; # future
+    iconv; # future
+    iconv_close; # future
+    iconv_open; # future
     syncfs; # future
 } LIBC_O;