Implement pthread_sigqueue.

Bug: http://b/112770187
Test: bionic-unit-tests
Change-Id: I03382cd5df2490b2e87265dba9007e2cb1b14cd2
diff --git a/libc/libc.x86.map b/libc/libc.x86.map
index d44001e..db86e55 100644
--- a/libc/libc.x86.map
+++ b/libc/libc.x86.map
@@ -1413,6 +1413,7 @@
     android_fdsan_get_tag_value;
     android_fdsan_get_error_level;
     android_fdsan_set_error_level;
+    pthread_sigqueue;
     timespec_get;
 } LIBC_P;