Implement PR ada/101385

For consistency's sake with -Wall & -w, this makes -Werror imply -gnatwe.

gcc/ada/
	PR ada/101385
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst
	(-Wall): Minor fixes.
	(-w): Likewise.
	(-Werror): Document that it also sets -gnatwe by default.
	* gcc-interface/lang-specs.h (ada): Expand -gnatwe if -Werror is
	passed and move expansion of -gnatw switches to before -gnatez.