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/malloc.h b/libc/include/malloc.h
index 2fa4b49..dc2ca2b 100644
--- a/libc/include/malloc.h
+++ b/libc/include/malloc.h
@@ -195,7 +195,11 @@
  *
  * Available since API level 23.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int malloc_info(int __must_be_zero, FILE* _Nonnull __fp) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
 
 /**
  * mallopt() option to set the decay time. Valid values are -1, 0 and 1.
@@ -368,7 +372,11 @@
  *
  * Available since API level 26.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int mallopt(int __option, int __value) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 /**
  * [__malloc_hook(3)](https://man7.org/linux/man-pages/man3/__malloc_hook.3.html)
@@ -379,6 +387,8 @@
  *
  * See also: [extra documentation](https://android.googlesource.com/platform/bionic/+/main/libc/malloc_hooks/README.md)
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 extern void* _Nonnull (*volatile _Nonnull __malloc_hook)(size_t __byte_count, const void* _Nonnull __caller) __INTRODUCED_IN(28);
 
 /**
@@ -413,5 +423,7 @@
  * See also: [extra documentation](https://android.googlesource.com/platform/bionic/+/main/libc/malloc_hooks/README.md)
  */
 extern void* _Nonnull (*volatile _Nonnull __memalign_hook)(size_t __alignment, size_t __byte_count, const void* _Nonnull __caller) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 __END_DECLS