seccomp: allow stat() for ubsan.

We've had complaints about ubsan issues for years, but never got to the
bottom of them, or saw them ourselves in testing. For some reason (still
not understood) we've started to see this ourselves in T and downstream
branches. So for now, let's just punch that extra hole.

Longer term, ubsan should stop needing any of this, so once
https://reviews.llvm.org/D124212 is in an LTS NDK, we should be able to
get rid of this _and_ the existing sanitizer-related holes.

Bug: android/ndk#1298
Bug: http://b/229989971
Test: treehugger
Change-Id: Id42cb29c4e943c0080c0d34ce4e5d6d1b32da9e8
(cherry picked from commit a0745ce)
Merged-In: Id42cb29c4e943c0080c0d34ce4e5d6d1b32da9e8

libc/SECCOMP_ALLOWLIST_COMMON.TXT

@@ -31,6 +31,8 @@ int	seccomp:seccomp(unsigned int operation, unsigned int flags, void *args)	all
 int open:open(const char*, int, ...)  arm,x86,x86_64
 int stat64:stat64(const char*, struct stat64*)  arm,x86
 ssize_t readlink:readlink(const char*, char*, size_t)  arm,x86,x86_64
+# Needed by ubsan in T? (http://b/229989971)
+int stat(const char*, struct stat*)  arm,x86,x86_64
 
 #
 # Useful new syscalls which we don't yet use in bionic.