* removed build type ASAN. Targets should define ASan usage by sanitize_address
  function
* compiler flags will be searched by compiler instead of per language
* FindASan warns, if a target can't be sanitized because of incompatible
  compilers
* added some helper functions

Thus C can be mixed with Fortran and the objects can be build with different
compilers, not both may support AddressSanitizer.

Instead of fix checking for C and CXX compilers, all enabled languages will be
tested now.

Older CMake versions are not capable of continue in foreach functions.