TrigOutputHandling: Fix compilation with clang12.
clang 12 properly requires --std=c++20 in order to handle ConstexprIterator. Get rid of the separate check on the clang version, and just check on the C++ feature symbol.
clang 12 properly requires --std=c++20 in order to handle ConstexprIterator. Get rid of the separate check on the clang version, and just check on the C++ feature symbol.