[flang] Add two new semantics tests for `critical-construct`

[ElliotWhitney]

Summary

Add two new semantics tests for `critical-construct` that test
addition standard conforming and non stardard conforming statements

[ktras]

LGTM. @ElliotWhitney, I don't believe you have push permissions, would you like me to push on your behalf?

[ElliotWhitney]

Yes, you can push it on my behalf thanks.

flang/test/Semantics/critical05.f90

+! RUN: %python %S/test_errors.py %s %flang_fc1
+program testcriticalconstruct
+  integer :: status
+  character(len=128) :: errormessage
+  integer :: total = 0
+  integer :: i
+
+  CRITICAL
+  END CRITICAL
+
+  Testname: Critical
+  End critical Testname
+
+  stat_variable: critical (STAT=status)
+  End critical stat_variable
+
+  errmsg_variable: critical (ERRMSG=errormessage)
+  End critical errmsg_variable
+
+  critical (ERRMSG=errormessage, STAT=status)
+  End critical
+
+  critical ()
+  end critical
+
+  critical (STAT=status)
+    do i = 1, this_image()
+        total = total + 1
+    end do
+    print *, "Total is: ", total
+  End critical
+
+  critical
+    10 continue
+    GO TO 10
+  End critical
+
+end program testcriticalconstruct

flang/test/Semantics/critical06.f90

+! RUN: %python %S/test_errors.py %s %flang_fc1
+program testcriticalconstruct
+
+  Start_name_only: Critical
+  !ERROR: CRITICAL construct name required but missing
+  End critical !C1117 in the Fortran 2018 standard
+
+  critical
+  !ERROR: CRITICAL construct name unexpected
+  end critical end_name_only !C1117 in Fortran 2018 standard
+
+end program