Adjust for new __sigaction_siginfo symbol.

Add symbol entries for the missing signal functions for the benefit of
autoconf. Autoconf compiles simple programs like:
char symbol();
int main() { return symbol(); }
To check if the symbol

Add symbol entries for the missing signal functions for the benefit of
autoconf. Autoconf compiles simple programs like:
char symbol();
int main() { return symbol(); }
To check if the symbol is present. This makes it happy.
Another way our symbol renaming breaks things.
This fixes gdb native build, which does not find sigprocmask otherwise
and fails to build because it finds pthread_sigmask() and not sigprocmask()!

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