Move the debug/signals.c (name to number / number to name) into util

[radare]

Also, current approach uses Sdb with hardcoded values for the signal name - signal number which is wrong because that thing depends on the target platform.

So maybe we should do this in a similar way syscalls are handled in r2. making them available in a cross-platform way.

for example 17 is sigchld on linux but sigstop on darwin

[stale]

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