Fortran/OpenMP: Fix strictly structured blocks parsing

gcc/fortran/ChangeLog:

	* parse.cc (parse_omp_structured_block): When parsing strictly
	structured blocks, issue an error if the end-directive comes
	before the 'end block'.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/strictly-structured-block-4.f90: New test.

gcc/fortran/parse.cc

@@ -5709,7 +5709,7 @@ parse_omp_structured_block (gfc_statement omp_st, bool workshare_stmts_only)
 	    }
 	  return st;
 	}
-      else if (st != omp_end_st)
+      else if (st != omp_end_st || block_construct)
 	{
 	  unexpected_statement (st);
 	  st = next_statement ();

gcc/testsuite/gfortran.dg/gomp/strictly-structured-block-4.f90

@@ -0,0 +1,21 @@
+! { dg-do compile }
+implicit none
+integer ::x,z
+x = 42
+print '(*(z16:" "))', loc(x)
+!$omp target map(x, z)
+block
+  integer :: y
+  x = 123
+  y = 99
+  !$omp target device(ancestor:1) map(always,tofrom:x) map(y) ! { dg-error "'ancestor' device modifier not preceded by 'requires' directive with 'reverse_offload' clause" }
+    print '(*(z16:" "))', loc(x), loc(y)
+    print * ,x, y
+    x = -x
+    y = -y
+  !$omp end target ! { dg-error "Unexpected ..OMP END TARGET statement" }
+  z = y
+end block
+    print * ,x !, z
+end
+