Documentation: Make OpenMP/OpenACC docs easier to find [PR26154]

PR c/26154 is one of our oldest documentation issues.  The only
discussion of OpenMP support in the GCC manual is buried in the "C
Dialect Options" section, with nothing at all under "Extensions".  The
Fortran manual does have separate sections for OpenMP and OpenACC
extensions so I have copy-edited/adapted that text for similar sections
in the GCC manual, as well as breaking out the OpenMP and OpenACC options
into their own section (they apply to all of C, C++, and Fortran).

I also updated the information about what versions of OpenMP and
OpenACC are supported and removed some redundant text from the Fortran
manual to prevent it from getting out of sync on future updates, and
inserted some cross-references to the new sections elsewhere.

gcc/c-family/ChangeLog
	PR c/26154
	* c.opt.urls: Regenerated.

gcc/ChangeLog
	PR c/26154
	* common.opt.urls: Regenerated.
	* doc/extend.texi (C Extensions): Adjust menu for new sections.
	(Attribute Syntax): Mention OpenMP directives.
	(Pragmas): Mention OpenMP and OpenACC directives.
	(OpenMP): New section.
	(OpenACC): New section.
	* doc/invoke.texi (Invoking GCC): Adjust menu for new section.
	(Option Summary): Move OpenMP and OpenACC options to their own
	category.
	(C Dialect Options): Move documentation for -foffload, -fopenacc,
	-fopenacc-dim, -fopenmp, -fopenmd-simd, and
	-fopenmp-target-simd-clone to...
	(OpenMP and OpenACC Options): ...this new section.  Light
	copy-editing of the option descriptions.

gcc/fortran/ChangeLog:
	PR c/26154
	* gfortran.texi (Standards): Remove redundant info about
	OpenMP/OpenACC standard support.
	(OpenMP): Copy-editing and update version info.
	(OpenACC): Likewise.
	* lang.opt.urls: Regenerated.