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/signal.h b/libc/include/signal.h
index 893fa9d..38dcbde 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -60,31 +60,73 @@
 #define si_timerid si_tid /* glibc compatibility. */
 
 int sigaction(int __signal, const struct sigaction* _Nullable __new_action, struct sigaction* _Nullable __old_action);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigaction64(int __signal, const struct sigaction64* _Nullable __new_action, struct sigaction64* _Nullable __old_action) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int siginterrupt(int __signal, int __flag);
 
 sighandler_t _Nonnull signal(int __signal, sighandler_t _Nullable __handler);
 int sigaddset(sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigaddset64(sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigdelset(sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigdelset64(sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigemptyset(sigset_t* _Nonnull __set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigemptyset64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigfillset(sigset_t* _Nonnull __set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigfillset64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 int sigismember(const sigset_t* _Nonnull __set, int __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigismember64(const sigset64_t* _Nonnull __set, int __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 int sigpending(sigset_t* _Nonnull __set);
-int sigpending64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
-int sigprocmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
-int sigprocmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
-int sigsuspend(const sigset_t* _Nonnull __mask);
-int sigsuspend64(const sigset64_t* _Nonnull __mask) __INTRODUCED_IN(28);
-int sigwait(const sigset_t* _Nonnull __set, int* _Nonnull __signal);
-int sigwait64(const sigset64_t* _Nonnull __set, int* _Nonnull __signal) __INTRODUCED_IN(28);
 
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigpending64(sigset64_t* _Nonnull __set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigprocmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigprocmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigsuspend(const sigset_t* _Nonnull __mask);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigsuspend64(const sigset64_t* _Nonnull __mask) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+int sigwait(const sigset_t* _Nonnull __set, int* _Nonnull __signal);
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int sigwait64(const sigset64_t* _Nonnull __set, int* _Nonnull __signal) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(26)
 int sighold(int __signal)
   __attribute__((__deprecated__("use sigprocmask() or pthread_sigmask() instead")))
   __INTRODUCED_IN(26);
@@ -97,6 +139,8 @@
   __INTRODUCED_IN(26);
 sighandler_t _Nonnull sigset(int __signal, sighandler_t _Nullable __handler)
   __attribute__((__deprecated__("use sigaction() instead"))) __INTRODUCED_IN(26);
+#endif /* __BIONIC_AVAILABILITY_GUARD(26) */
+
 
 int raise(int __signal);
 int kill(pid_t __pid, int __signal);
@@ -110,17 +154,41 @@
 
 int pthread_kill(pthread_t __pthread, int __signal);
 #if defined(__USE_GNU)
+
+#if __BIONIC_AVAILABILITY_GUARD(29)
 int pthread_sigqueue(pthread_t __pthread, int __signal, const union sigval __value) __INTRODUCED_IN(29);
+#endif /* __BIONIC_AVAILABILITY_GUARD(29) */
+
 #endif
 
 int pthread_sigmask(int __how, const sigset_t* _Nullable __new_set, sigset_t* _Nullable __old_set);
-int pthread_sigmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
 
+#if __BIONIC_AVAILABILITY_GUARD(28)
+int pthread_sigmask64(int __how, const sigset64_t* _Nullable __new_set, sigset64_t* _Nullable __old_set) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int sigqueue(pid_t __pid, int __signal, const union sigval __value) __INTRODUCED_IN(23);
 int sigtimedwait(const sigset_t* _Nonnull __set, siginfo_t* _Nullable __info, const struct timespec* _Nullable __timeout) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigtimedwait64(const sigset64_t* _Nonnull __set, siginfo_t* _Nullable __info, const struct timespec* _Nullable __timeout) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(23)
 int sigwaitinfo(const sigset_t* _Nonnull __set, siginfo_t* _Nullable __info) __INTRODUCED_IN(23);
+#endif /* __BIONIC_AVAILABILITY_GUARD(23) */
+
+
+#if __BIONIC_AVAILABILITY_GUARD(28)
 int sigwaitinfo64(const sigset64_t* _Nonnull __set, siginfo_t* _Nullable __info) __INTRODUCED_IN(28);
+#endif /* __BIONIC_AVAILABILITY_GUARD(28) */
+
 
 /**
  * Buffer size suitable for any call to sig2str().
@@ -137,6 +205,8 @@
  *
  * Available since API level 36.
  */
+
+#if __BIONIC_AVAILABILITY_GUARD(36)
 int sig2str(int __signal, char* _Nonnull __buf) __INTRODUCED_IN(36);
 
 /**
@@ -149,6 +219,8 @@
  * Available since API level 36.
  */
 int str2sig(const char* _Nonnull __name, int* _Nonnull __signal) __INTRODUCED_IN(36);
+#endif /* __BIONIC_AVAILABILITY_GUARD(36) */
+
 
 __END_DECLS