gdb: delete SYMBOL_SECTION and MSYMBOL_SECTION macros

Delete two more symbol/section related macros.  This time it's
SYMBOL_SECTION and MSYMBOL_SECTION.

As with general_symbol_info::m_name it is not currently possible to
make general_symbol_info::m_section private as general_symbol_info
must remain a POD type.

But other than failing to make the new m_section private, this change
does what you'd expect, adds a get and set member function and updates
all users to use the new functions instead of the previous wrapper
macros.

There should be no user visible change after this commit.

gdb/ChangeLog:

	* coff-pe-read.c (add_pe_forwarded_sym): Make use of section_index
	and set_section_index member functions where appropriate.
	* coffread.c (coff_symtab_read): Likewise.
	(process_coff_symbol): Likewise.
	* ctfread.c (set_symbol_address): Likewise.
	* dwarf2/read.c (add_partial_symbol): Likewise.
	(var_decode_location): Likewise.
	* language.c: Likewise.
	* minsyms.c (minimal_symbol_reader::record_full): Likewise.
	(compact_minimal_symbols): Likewise.
	(minimal_symbol_upper_bound): Likewise.
	* objfiles.c (relocate_one_symbol): Likewise.
	* psympriv.h (partial_symbol::obj_section): Likewise.
	(partial_symbol::address): Likewise.
	* psymtab.c (partial_symtab::add_psymbol): Likewise.
	* stabsread.c (scan_file_globals): Likewise.
	* symmisc.c (dump_msymbols): Likewise.
	* symtab.c (general_symbol_info::obj_section): Likewise.
	(fixup_section): Likewise.
	(get_msymbol_address): Likewise.
	* symtab.h (general_symbol_info::section): Rename to...
	(general_symbol_info::m_section): ...this.
	(general_symbol_info::set_section_index): New member function.
	(general_symbol_info::section_index): Likewise.
	(SYMBOL_SECTION): Delete.
	(MSYMBOL_VALUE_ADDRESS): Make use of section_index and
	set_section_index member functions where appropriate.
	(MSYMBOL_SECTION): Delete.
	(symbol::symbol): Update to initialize 'm_section'.
	* xcoffread.c (read_xcoff_symtab): Make use of set_section_index.
	(process_xcoff_symbol): Likewise.

gdb/coff-pe-read.c

@@ -246,7 +246,7 @@ add_pe_forwarded_sym (minimal_symbol_reader &reader,
 
   vma = BMSYMBOL_VALUE_ADDRESS (msymbol);
   msymtype = MSYMBOL_TYPE (msymbol.minsym);
-  section = MSYMBOL_SECTION (msymbol.minsym);
+  section = msymbol.minsym->section_index ();
 
   /* Generate a (hopefully unique) qualified name using the first part
      of the dll name, e.g. KERNEL32!AddAtomA.  This matches the style