Linking of an enabled ghost unit which requires a finalizer lead to an
error, as the name generated by the binder for calling the finalizer was
not the same as the name chosen by the compiler. Now fixed.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-07-23  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* exp_ch7.adb (Create_Finalizer): Force finalizer not to be
	Ghost enabled.
	* exp_dbug.adb (Get_External_Name): Explain special case of
	Ghost finalizer.

gcc/testsuite/

	* gnat.dg/ghost6.adb, gnat.dg/ghost6_pkg.ads: New testcase.