* coffread.c, dbxread.c, elfread.c, mipsread.c, nlmread.c,

	* coffread.c, dbxread.c, elfread.c, mipsread.c, nlmread.c,
	os9kread.c: Replace identical sym_offsets functions with
	default_symfile_offsets.
	* somread.c (som_symfile_offsets): Use new SIZEOF_SECTION_OFFSETS
	macro to allocate section_offsets.
	* symfile.c (default_symfile_offsets): New function.
	* symfile.h: Declare default_symfile_offsets.
	* symtab.h: Define SIZEOF_SECTION_OFFSETS macro to
	simplify allocation of section_offsets.