ld: doc: Use consistent language for 'PE target'-only options

It seems like the 'i386 PE targeted' phrasing probably predates x86_64
PE support in binutils, and should have been touched when that was
added.

Even loosely interpreting that phrase to mean 'those two Intel
architectures, you know what I mean', this is less than helpful now that
PE aarch64 is a possibility.

Change the use of various phrases like '[This is an i386 PE specific
option]' to conistently use '[This option is specific to PE targeted
ports of the linker]' nearly everywhere.

The only options that really are specific in this way are
'--large-address-aware' (PE only) and '--high-entropy-va' (PE+ only), so
annotate those appropriately.

Do an editing pass of the various other mentions of 'PE'.

Also, add the 'PE only' annotation to the description of
'--leading-underscore' in the 'Options Specific to PE Targets' section,
to be consistent with all the others.

Also, since we've already mentioned that all the DllCharacteristics
flags are PE-specific, don't awkwardly mention it (again) as part of the
note about what Windows version support for that flag was introduced in.

Future work: the phrase 'PE targeted port of the linker' seems a bit
off, since cross-tools are a thing. Should it just be 'PE targeted linker'?

2026-06-01  Jon Turney  <jon.turney@dronecode.org.uk>

	* ld.texi (Options): Use consistent language for 'PE target'-only
	options.