[Ada] Avoid to close irrelevant file descriptors

[Ada] Avoid to close irrelevant file descriptors

'Close' subprogram of GNAT.Expect can close irrelevant file descriptors
when 'Expect' was terminated by Process_Died exception and any file open
operations was done before call to 'Close'.

2019-09-17  Vadim Godunko  <godunko@adacore.com>

gcc/ada/

	* libgnat/g-expect.ads, libgnat/g-expect.adb (Close_Input): New
	subprogram.
	(Get_Command_Output): Call Close_Input to close input stream.
	(Expect_Internal): Likewise.
	(Close): Likewise.
	* libgnat/g-exptty.adb (Close): Likewise.

gcc/testsuite/

	* gnat.dg/expect3.adb: New testcase.

From-SVN: r275781