Enable --use-header by default and remove the corresponding command-line option.
Just as stated.
The current behavior of
valac is to always generate the header file internally and
store it if a
header_filename has been set. However,
ValaCCodeBaseModule.add_symbol_declaration will ignore this header file if
--use-header is not enabled and return
false, forcing the various
generate_*_definition methods to put symbol definitions in the C files.
Here I update
ValaCodeContext.use_header to evaluate as
true whenever a header file exists, so that
add_symbol_declaration and other files that check for a header will behave appropriately.