Add syncline support and location accessor to internal %define

Add syncline support and location accessor to internal %define
interfaces.
* data/bison.m4 (b4_percent_define_get_loc): New.
(b4_percent_define_get_syncline): New.
(b4_percent_define_flag_if): Use b4_percent_define_get_loc.
(b4_percent_define_default): Record defining location as line 1 rather
than 0 for the sake of synchronizing #line's, and define
b4_percent_define_syncline(VARIABLE).
(b4_percent_define_check_values): Use b4_percent_define_get_loc.
* src/muscle_tab.c (muscle_syncline_grow): New.
(muscle_code_grow): Use muscle_syncline_grow.
(muscle_percent_define_insert): Use muscle_percent_define_get_loc, and
define b4_percent_define_syncline(VARIABLE).
(muscle_percent_define_get_loc): New.
(muscle_percent_define_get_syncline): New.
(muscle_percent_define_flag_if): Use muscle_percent_define_get_loc, and
remove some unused variables.
(muscle_percent_define_default): Record defining location as line 1
rather than 0 for the sake of synchronizing #line's, and define
b4_percent_define_syncline(VARIABLE).
(muscle_percent_define_check_values): Use
muscle_percent_define_get_loc.
* src/muscle_tab.h (muscle_percent_define_get_loc): Prototype.
(muscle_percent_define_get_syncline): Prototype.
* tests/skeletons.at (%define Boolean variables: invalid skeleton
defaults): Update output for location change.
(Complaining during macro argument expansion): Extend to test
b4_percent_define_get_loc and b4_percent_define_get_syncline errors.