S/390: Document z14/arch12 -march option.

gcc/ChangeLog:

2018-11-26  Andreas Krebbel  <krebbel@linux.ibm.com>

	* doc/invoke.texi: Document z14/arch12 -march option.

From-SVN: r266462

gcc/ChangeLog

+2018-11-26  Andreas Krebbel  <krebbel@linux.ibm.com>
+
+	* doc/invoke.texi: Document z14/arch12 -march option.
+
 2018-11-25  Sandra Loosemore  <sandra@codesourcery.com>
 
 	PR c/57166

gcc/doc/invoke.texi

@@ -25925,8 +25925,8 @@ Generate code that runs on @var{cpu-type}, which is the name of a
 system representing a certain processor type.  Possible values for
 @var{cpu-type} are @samp{z900}/@samp{arch5}, @samp{z990}/@samp{arch6},
 @samp{z9-109}, @samp{z9-ec}/@samp{arch7}, @samp{z10}/@samp{arch8},
-@samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11}, and
-@samp{native}.
+@samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11},
+@samp{z14}/@samp{arch12}, and @samp{native}.
 
 The default is @option{-march=z900}.