[flang] Convert RUNTIME_CHECK to better error for user errors in transformational.cpp

In flang/runtime/transformational.cpp, there are many RUNTIME_CHECK assertions
for errors that should have been caught in semantics, but there are alno others
that signify program errors that in principle cannot be detected until
execution.  Convert this second group into readable fatal error messages.
Also clean up some missing braces and incorrect printf formats found
along the way.

Differential Revision: https://reviews.llvm.org/D122037