API guard every post-21 API.

This was generated mechanically by reverting my recent re-hide commits
(except for mempcpy, but versioner cleaned that up for me anyway),
reverting the commits which removed versioner, then:

```
m out/soong/ndk_headers.timestamp
cp -r out/soong/ndk/sysroot/usr/include/* bionic/libc/include
git -C bionic clean -df
```

Effectively, this has restored the `versioner` processed headers, but
I'm checking the results of that in so we don't have to keep
`versioner` around.

For the NDK, this restores r27 behavior by default. Anyone that's
opted into weak APIs will get the new behavior. I think this is our
best option. Anyone writing code with Android in mind should be using
weak APIs, but any code being lightly ported (and thus using the
default configuration) should not be, and it's those ports where we're
having trouble with collisions.

Bug: https://github.com/android/ndk/issues/2081
Test: None
Change-Id: I370079d27566b0c1543fb5890c958c8d09b05006
diff --git a/libc/include/netdb.h b/libc/include/netdb.h
index 88214d5..04aaf5c 100644
--- a/libc/include/netdb.h
+++ b/libc/include/netdb.h
@@ -212,28 +212,52 @@
 void herror(const char* _Nonnull __s);
 const char* _Nonnull hstrerror(int __error);
 struct hostent* _Nullable gethostbyaddr(const void* _Nonnull __addr, socklen_t __length, int __type);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int gethostbyaddr_r(const void* _Nonnull __addr, socklen_t __length, int __type, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 struct hostent* _Nullable gethostbyname(const char* _Nonnull __name);
 int gethostbyname_r(const char* _Nonnull __name, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr);
 struct hostent* _Nullable gethostbyname2(const char* _Nonnull __name, int __af);
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int gethostbyname2_r(const char* _Nonnull __name, int __af, struct hostent* _Nonnull __ret, char* _Nonnull __buf, size_t __buf_size, struct hostent* _Nullable * _Nonnull __result, int* _Nonnull __h_errno_ptr) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 void endhostent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct hostent* _Nullable gethostent(void);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 void sethostent(int __stay_open) __INTRODUCED_IN(28);
 
 /* These functions are obsolete. None of these functions return anything but nullptr. */
 void endnetent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct netent* _Nullable getnetbyaddr(uint32_t __net, int __type);
 struct netent* _Nullable getnetbyname(const char* _Nonnull __name);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 struct netent* _Nullable getnetent(void) __INTRODUCED_IN(28);
 void setnetent(int __stay_open) __INTRODUCED_IN(28);
 
 /* None of these functions return anything but nullptr. */
 void endprotoent(void) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 struct protoent* _Nullable getprotobyname(const char* _Nonnull __name);
 struct protoent* _Nullable getprotobynumber(int __proto);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 struct protoent* _Nullable getprotoent(void) __INTRODUCED_IN(28);
 void setprotoent(int __stay_open) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /* These functions return entries from a built-in database. */
 void endservent(void);