[flang] Allocate semantic checks (second part)

Implement semantic checks and realted tests for constraints:
C937, C938, C939, C940, C941, C942, C945 (second part),
C946, C947, C948, C949 and C950.

Original-commit: flang-compiler/f18@b4965d272b1749d554e3d1388c0a7856591741e8
Tree-same-pre-rewrite: false