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.x86.map b/libc/libc.x86.map
index 8f6c64e..6838184 100644
--- a/libc/libc.x86.map
+++ b/libc/libc.x86.map
@@ -1257,6 +1257,7 @@
 LIBC_O {
   global:
     getdomainname;
+    hasmntopt;
     pthread_getname_np;
     setdomainname;
 } LIBC_N;