Don't emit whitespace when stringifying TOKEN_WHITE.
Other aspects of the preprocessor already skip whitespace leading up to a token. The only situation in which a TOKEN_WHITE can
exist as part of the token stream during stringification, is when the whitespace is trailing after a token. This is situation is
really only possible in the context of a macro argument. This behaviour is inconsistent.

Consider the following
FOO( space_before)
FOO(space_after )

The former will reduce to "space_before" since the preprocessor will skip whitespace leading up to the token `space_before', while
the latter will reduce to "space_after ".

The C preprocessor doesn't preserve whitespace, so we won't either. This doesn't break any existing code.