Add `struct sigaction64` and `sigaction64`.

Bug: http://b/72493232
Test: ran tests
Change-Id: I47b0560a30aa33a9b1f1978dfb7f84d2e3d389b8
diff --git a/libc/libc.mips.map b/libc/libc.mips.map
index c364608..2a93132 100644
--- a/libc/libc.mips.map
+++ b/libc/libc.mips.map
@@ -1370,6 +1370,7 @@
     sethostent;
     setnetent;
     setprotoent;
+    sigaction64;
     sigaddset64;
     sigdelset64;
     sigemptyset64;