[Darwin] Revert one hunk from r273016 (TLC for older Darwin versions).

t-darwin8 is nolonger needed (or present) for pre-10.4 powerpc, so remove
the reference.

2019-07-04  Iain Sandoe  <iain@sandoe.co.uk>

	* config.host: Remove reference to t-darwin8.

From-SVN: r273091

libgcc/ChangeLog

+2019-07-04  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* config.host: Remove reference to t-darwin8.
+
 2019-07-03  Iain Sandoe  <iain@sandoe.co.uk>
 
 	* config.host (powerpc-*-darwin*,powerpc64-*-darwin*): Revise crt

libgcc/config.host

@@ -1084,11 +1084,9 @@ powerpc-*-darwin*)
 	case ${host} in
 	*-*-darwin9* | *-*-darwin[12][0-9]*)
 	  # libSystem contains unwind information for signal frames since
-	  # Darwin 9.  We don't need longcall either.
+	  # Darwin 9.
 	  ;;
 	*)
-	  # prepend the fragment forcing darwin8 codegen.
-	  tmake_file="rs6000/t-darwin8 $tmake_file"
 	  md_unwind_header=rs6000/darwin-unwind.h
 	  ;;
 	esac