Update c standard for Trillinos from c99 to c11.

Created by: prwolfe

A number of trillinos files do not compile cleanly with c99 and since we are using c++11 I think it would be best to simply advance the c standard as well. This was previously addressed in #1810 and #1974

@trilinos

Expectations

All Trilinos codes should build without warnings and links should be expected to complete or fail based on the language specification given.

Current Behavior

Builds contain functions that are not available in c99. That creates a warning for an implicit function declaration, and then the link resolves the symbol from the (currently common) standard library. There is nothing guaranteeing that the symbol will continue to be available.

Motivation and Context

Sierra builds are done with warnings-as-errors=on, so all these warnings cause build failures.

Definition of Done

• Decide on a common standard for the c language between all the SART codes.
• Enforce that standard across all codes.