Add hasmntopt(3)

bionic has the Linux-specific mntent.h but is missing hasmntopt().

Change-Id: I0ab7b83626c969704add4e64b37a6fc715d4a723
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/libc/libc.mips.brillo.map b/libc/libc.mips.brillo.map
index c5b1bd3..7133f4b 100644
--- a/libc/libc.mips.brillo.map
+++ b/libc/libc.mips.brillo.map
@@ -1258,6 +1258,7 @@
 LIBC_O {
   global:
     getdomainname;
+    hasmntopt;
     pthread_getname_np;
     setdomainname;
 } LIBC_N;