[Darwin, PPC, committed] Install the same headers as other sub-targets.

[Iain Sandoe]

This is primarily in order to improve testsuite coverage, (it allows us to run
the compile tests for the x86 intrinisics support, for example).  We might
elect to prune the list at some point.

tested on powerpc-darwin9
applied to mainline
Iain

2019-06-28  Iain Sandoe  <i...@sandoe.co.uk>

        * config.gcc (powerpc-*-darwin*, powerpc64-*-darwin*): Remove
        override on extra_headers.

diff --git a/gcc/config.gcc b/gcc/config.gcc
index 8e3285b..c281c41 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -2627,13 +2627,11 @@ powerpc-*-darwin*)
            ;;
        esac
        tmake_file="${tmake_file} t-slibgcc"
-       extra_headers=altivec.h
        ;;
 powerpc64-*-darwin*)
        extra_options="${extra_options} ${cpu_type}/darwin.opt"
        tmake_file="${tmake_file} ${cpu_type}/t-darwin64 t-slibgcc"
        tm_file="${tm_file} ${cpu_type}/darwin8.h ${cpu_type}/darwin64.h"
-       extra_headers=altivec.h
        ;;
 powerpc*-*-freebsd*)
        tm_file="${tm_file} dbxelf.h elfos.h gnu-user.h ${fbsd_tm_file} 
rs6000/sysv4.h"