Implement `createSanitizerCtor`, common helper function for all sanitizers

Summary:
This helper function creates a ctor function, which calls sanitizer's
init function with given arguments. This constructor is then expected
to be added to module's ctors. The patch helps unifying how sanitizer
constructor functions are created, and how init functions are called
across all sanitizers.

Reviewers: kcc, samsonov

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8777

llvm-svn: 236627