[Darwin] Fix PR87030 add missed commit hunks.

[Darwin] Fix PR87030 add missed commit hunks.

Messed up the commit, and missed changes to gcc/config.gcc and to the comments
in some of the headers.

2019-07-24  Iain Sandoe  <iain@sandoe.co.uk>

gcc/

	PR bootstrap/87030
	* config/i386/darwin.h (REAL_LIBGCC_SPEC): Move from here...
	* config/i386/darwin32-biarch.h .. to here.
	* config/i386/darwin64-biarch.h: Adjust comments.
	* config/rs6000/darwin32-biarch.h: Likewise.
	* config/rs6000/darwin64-biarch.h: Likewise.
	* config.gcc: Missed commit from r273746
	(*-*-darwin*): Don't include CPU t-darwin here.
	(i[34567]86-*-darwin*): Adjust to use biarch files. Produce
	an error message if i686-darwin configuration is attempted for
	Darwin >= 18.

From-SVN: r273749