Fix libgomp.oacc-c-c++-common/pr84217.c for C++

	* testsuite/libgomp.oacc-c-c++-common/pr84217.c (abort)
	[__cplusplus]: Declare extern "C".

From-SVN: r257457

libgomp/ChangeLog

+2018-02-07  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
+
+	* testsuite/libgomp.oacc-c-c++-common/pr84217.c (abort)
+	[__cplusplus]: Declare extern "C".
+
 2018-02-07  Tom de Vries  <tom@codesourcery.com>
 
 	PR libgomp/84217

libgomp/testsuite/libgomp.oacc-c-c++-common/pr84217.c

-extern void abort (void);
+extern
+#ifdef __cplusplus
+"C"
+#endif
+void abort (void);
 
 #define N 10