Implement pthread_sigqueue.

Bug: http://b/112770187
Test: bionic-unit-tests
Change-Id: I03382cd5df2490b2e87265dba9007e2cb1b14cd2
diff --git a/libc/include/signal.h b/libc/include/signal.h
index 00860d5..9d1030a 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -113,6 +113,10 @@
 void psignal(int __signal, const char* __msg) __INTRODUCED_IN(17);
 
 int pthread_kill(pthread_t __pthread, int __signal);
+#if defined(__USE_GNU)
+int pthread_sigqueue(pthread_t __pthread, int __signal, const union sigval __value) __INTRODUCED_IN(__ANDROID_API_Q__);
+#endif
+
 int pthread_sigmask(int __how, const sigset_t* __new_set, sigset_t* __old_set);
 int pthread_sigmask64(int __how, const sigset64_t* __new_set, sigset64_t* __old_set) __INTRODUCED_IN(28);