doc/gccgo: update gcc status, remove double spaces
doc/gccgo: update gcc status, remove double spaces

This change updates the status of gccgo 8 and gccgo 9, which are now
released.

It also replaces every instance of two-spaces with one space in text
paragraphs, which is the preferred style in Go documentation.

Fixes #34167

Change-Id: I94a4d85c06281f2623d39a68db7b6c95b5867999
Reviewed-on: https://go-review.googlesource.com/c/go/+/193842
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/go,akutz/go,nawawi/go,akutz/go,akutz/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,akutz/go,akutz/go,akutz/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,golang/go,golang/go,golang/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,golang/go,CAFxX/go