contrib.texi, [...]: Capitalize "gcc", "g++" and "g77" or mark up with appropriate markup.

	* doc/contrib.texi, doc/extend.texi, doc/gcov.texi,
	doc/install.texi, doc/invoke.texi, doc/makefile.texi,
	doc/sourcebuild.texi, doc/tm.texi, doc/trouble.texi: Capitalize
	"gcc", "g++" and "g77" or mark up with appropriate markup.  Adjust
	wording and grammar.

From-SVN: r79482