gas: fold is_end_of_line[] into lex_type[]

... by way of introducing LEX_EOL and LEX_EOS. As a prereq convert the
remaining open-coded accesses.

The Alpha change is actually a functional one: The array slot for '!'
having been set to 1 is very unlikely to have been correct. 1 means "end
of line", when surely "end of statement" was always meant.