darwin, powerpc - set .machine in an asm file.

The asm file fails to build if we use a modern assembler
which checks that the machine is consistent with the 
filetype.  Fixed by adjusting in a similar manner to 
other assembler.

libgcc/

2019-05-12  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/darwin-vecsave.S: Set .machine appropriately.

From-SVN: r271111

libgcc/ChangeLog

+2019-05-12  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* config/rs6000/darwin-vecsave.S: Set .machine appropriately.
+
 2019-05-07  Hongtao Liu  <hongtao.liu@intel.com>
 
 	* config/i386/cpuinfo.c (get_available_features): Detect BF16.

libgcc/config/rs6000/darwin-vecsave.S

@@ -31,8 +31,14 @@
    (4 bytes) to do the operation; for Vector regs, 2 instructions are
    required (8 bytes.).   */
 
+/* With some assemblers, we need the correct machine directive to get the
+   right CPU type / subtype in the file header.  */
+#if	__ppc64__
+	.machine ppc64
+#else
 	.machine ppc7400
-.text
+#endif
+	.text
 	.align 2
 
 .private_extern saveVEC