This patch allows the compiler to report an error on Bit_Order when
defined for a record extension.

2018-07-16  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* sem_ch13.adb (Analyze_Attribute_Definition_Clause): Report an error
	on Bit_Order when defined for a record extension.

gcc/testsuite/

	* gnat.dg/bit_order1.adb: New testcase.

From-SVN: r262712