An option is added to the check to select wich set of functions is
defined as asynchronous-safe functions.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D90851
SIG30-C. Call only asynchronous-safe functions within signal handlers
First version of this check, only minimal list of functions is allowed
("strictly conforming" case), for C only.
Differential Revision: https://reviews.llvm.org/D87449