[Patch, build, ppc] allow ppc config "--with-mcpu=native"

[Iain Sandoe]

Hi,

The PPC port can handle -mcpu=native.
The patch below enables its use at config time,
OK for trunk?
thanks,
Iain

gcc:

        * config.gcc (powerpc*-*-* | rs6000-*-*): Allow 'native' as a
        valid configured CPU choice.

Index: gcc/config.gcc
===================================================================
--- gcc/config.gcc      (revision 189745)
+++ gcc/config.gcc      (working copy)
@@ -3285,7 +3285,7 @@
                                tm_defines="${tm_defines} CONFIG_PPC405CR"
                                eval "with_$which=405"
                                ;;
-                       "" | common \
+                       "" | common | native \
                        | power | power[234567] | power6x | powerpc | powerpc64 
\
                        | rios | rios1 | rios2 | rsc | rsc1 | rs64a \
                        | 401 | 403 | 405 | 405fp | 440 | 440fp | 464 | 464fp \