fixed noexept warnings (#632)
fixed noexept warnings (#632)

* fixed noexept warnings

- Removed conditional compilation for throwing version of GSL
  vs fail_fast because we don't want users of the code to see
  differences in the span interface dependent on error mechanism
  chosen
- Removed noexcept from functions that may fail at runtime
- Fixed CppCoreCheck warnings related to missing and incorrect
  noexcept
- do not warn on unnown attributes for GCC and Clang

* remove suppress that does not compiler for clang and gcc

neilmacintosh/GSL