libgettextpo: Remove static variable gram_pos.

libgettextpo: Remove static variable gram_pos.

* gettext-tools/src/po-gram.h (struct po_parser_state): Add field gram_pos.
* gettext-tools/src/po-lex.h (gram_pos): Remove declaration.
* gettext-tools/src/po-lex.c (gram_pos): Remove variable.
(po_gram_error, lex_start, lex_end, lex_getc, lex_ungetc, keyword_p,
po_gram_lex): Access ps->gram_pos instead of gram_pos.
* gettext-tools/src/po-gram-gen.y: Access ps->gram_pos instead of gram_pos.
* gettext-tools/woe32dll/gettextsrc-exports.c (gram_pos): Remove export.