[PATCH] Add support for -fsanitize-blacklist and default blacklists for DFSan

[Kostya Serebryany]

  The code is fine, feel free to commit it now if it blocks you.
  But the design may deserve more discussion; would you like to do it here?
  My first question: what happens if a pointer to a libc function is taken?

  char (*f)(const char*);
  if (...) f = &strdup();  // from libc
  else   f = &my_strdup(); // instrumented
  f();  // either libc or my code is called.

http://llvm-reviews.chandlerc.com/D1346