[flang] More semantic checking for DO constructs

This time I'm adding to the checks for constraint C1137, which states
that image control statements cannot appear in a DO CONCURRENT.  The
checks I added test to see if the DO CONCURRENT contains an ALLOCATE or
DEALLOCATE that references a coarray.

Original-commit: flang-compiler/f18@c16b883db3016bceb2c795babe047d297ba92717
Reviewed-on: https://github.com/flang-compiler/f18/pull/769