ada: Improve test for unprocessed preprocessor directives

ada: Improve test for unprocessed preprocessor directives

Preprocessor directives are case insensitive and may have spaces or tabs
between the '#' and the keyword. When checking for the error case of
unprocessed preprocessor directives, take these rules into account.

gcc/ada/

	* scng.adb (scan): When checking for an unprocessed preprocessor
	directive, take into account the preprocessor's rules about case
	insensitivity and about white space between the '#' and the
	keyword.