re PR testsuite/62250 (FAIL: gfortran.dg/coarray/alloc_comp_1.f90 -fcoarray=lib -O2 -lcaf_single)

	PR testsuite/62250
	* lib/target-supports.exp (check_effective_target_libatomic_available):
	New.
	* gfortran.dg/coarray/caf.exp: Only add -latomic for
	targets that match effective-target libatomic_available.
	* gfortran.dg/coarray_lib_comm_1.f90: Similar.

From-SVN: r219365

gcc/testsuite/gfortran.dg/coarray_lib_comm_1.f90

 ! { dg-do run }
-! { dg-options "-fdump-tree-original -fcoarray=lib -lcaf_single -latomic" }
+! { dg-options "-fdump-tree-original -fcoarray=lib -lcaf_single -latomic" { target libatomic_available } }
+! { dg-options "-fdump-tree-original -fcoarray=lib -lcaf_single" { target { ! libatomic_available } } }
 !
 ! Some dependency-analysis check for coarray communication
 !