ld: Extend documentation for EXCLUDE_FILE

ld: Extend documentation for EXCLUDE_FILE

There was a gap in the documentation of EXCLUDE_FILE that could cause
confusion to a user.  When writing an input section specifier like this:

    *(EXCLUDE_FILE (somefile.o) .text .text.*)

this could mean one of the following:

   1. All '.text' and '.text.*' from all files except for 'somefile.o',
   or
   2. All '.text' from all files except 'somefile.o', and all '.text.*'
   sections from all files.

It turns out that the second interpretation is correct, but the manual
does not make this clear (to me at least).  Hopefully this patch makes
things clearer.

ld/ChangeLog:

	* ld/ld.texinfo (Input Section Basics): Expand the description of
	EXCLUDE_FILE.