[Ada] Mention GNAT Studio instead of GPS

[Ada] Mention GNAT Studio instead of GPS

2019-10-10  Anthony Leonardo Gracio  <leonardo@adacore.com>

gcc/ada/

	* doc/gnat_ugn/about_this_guide.rst,
	doc/gnat_ugn/building_executable_programs_with_gnat.rst,
	doc/gnat_ugn/getting_started_with_gnat.rst,
	doc/gnat_ugn/gnat_and_program_execution.rst, errout.ads,
	exp_ch3.adb, gnatls.adb, impunit.adb, lib-writ.ads, opt.ads,
	sem_ch7.adb, sem_prag.adb, sem_res.adb, sem_warn.adb,
	terminals.c: Replace GPS by GNAT Studio.
	* gnat_ugn.texi: Regenerate.

From-SVN: r276815