Add `struct sigaction64` and `sigaction64`.

Bug: http://b/72493232
Test: ran tests
Change-Id: I47b0560a30aa33a9b1f1978dfb7f84d2e3d389b8
diff --git a/libc/libc.arm64.map b/libc/libc.arm64.map
index 3af0d42..a39a233 100644
--- a/libc/libc.arm64.map
+++ b/libc/libc.arm64.map
@@ -1306,6 +1306,7 @@
     sethostent;
     setnetent;
     setprotoent;
+    sigaction64;
     sigaddset64;
     sigdelset64;
     sigemptyset64;