Make symtab.c better styled.

Make symtab.c better styled.

Note that print_msymbol_info does not (yet?) print data msymbol
using variable_name_style, as otherwise 'info variables'
would show the non debugging symbols in variable name style,
but 'real' variables would be not styled.

2019-02-12  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* symtab.h (struct minimal_symbol data_p): New const method.
	(struct minimal_symbol text_p): Likewise.
	* symtab.c (output_source_filename): Use file name style
	to print file name.
	(print_symbol_info): Likewise.
	(print_msymbol_info): Use address style to print addresses.
	Use function name style to print executable text symbols.
	(expand_symtab_containing_pc): Use data_p.
	(find_pc_sect_compunit_symtab): Likewise.