[libgomp, openacc, testsuite] Fix async logic in lib-12.f90

In testcase lib-12.f90, all acc_async_test calls are placed in a location
where they are not guaranteed to succeed, which explains why there's an xfail
for the lower optimization levels.

This patch fixes the problem by moving the acc_async_test calls to the correct
locations.

Reg-tested on x86_64 with nvptx accelerator.

2018-07-26  Tom de Vries  <tdevries@suse.de>

	* testsuite/libgomp.oacc-fortran/lib-12.f90: Move acc_async_test calls
	to correct locations.  Remove xfail.

From-SVN: r262990

libgomp/ChangeLog

 2018-07-26  Tom de Vries  <tdevries@suse.de>
 
+	* testsuite/libgomp.oacc-fortran/lib-12.f90: Move acc_async_test calls
+	to correct locations.  Remove xfail.
+
+2018-07-26  Tom de Vries  <tdevries@suse.de>
+
 	* testsuite/libgomp.oacc-fortran/lib-13.f90: Replace acc_wait_all with
 	acc_wait.  Move acc_async_test calls to correct locations.  Remove
 	xfail.

libgomp/testsuite/libgomp.oacc-fortran/lib-12.f90

 ! { dg-do run }
-! { dg-xfail-run-if "TODO" { openacc_nvidia_accel_selected } { "-O0" "-O1" } { "" } }
 
 program main
   use openacc
@@ -18,10 +17,9 @@ program main
 
   call acc_wait_async (0, 1)
 
-  if (acc_async_test (0) .neqv. .TRUE.) call abort
+  call acc_wait (1)
 
+  if (acc_async_test (0) .neqv. .TRUE.) call abort
   if (acc_async_test (1) .neqv. .TRUE.) call abort
 
-  call acc_wait (1)
-
 end program