powerpc: Fix unrecognized instruction errors with recent binutils

Recent versions of binutils (with commit
b25f942e18d6ecd7ec3e2d2e9930eb4f996c258a) stopped preserving "sticky"
options across a base `.machine` directive, nullifying the use of
passing "-many" through GCC to the assembler.  As a result, some
instructions which were recognized even under older, more stringent
`.machine` directives become unrecognized instructions in that
context.

In `sysdeps/powerpc/tst-set_ppr.c`, the use of the `mfppr32` extended
mnemonic became unrecognized, as the default compilation with GCC for
32bit powerpc adds a `.machine ppc` in the resulting assembly, so the
command line option `-Wa,-many` is essentially ignored, and the ISA 2.06
instructions and mnemonics, like `mfppr32`, are unrecognized.

The compilation of `sysdeps/powerpc/tst-set_ppr.c` fails with:
Error: unrecognized opcode: `mfppr32'

Add appropriate `.machine` directives in the assembly to bracket the
`mfppr32` instruction.

Part of a 2019 fix (commit 9250e6610f) to
the above test's Makefile to add `-many` to the compilation when GCC
itself stopped passing `-many` to the assember no longer has any effect,
so remove that.

Reported-by: Joseph Myers <joseph@codesourcery.com>

sysdeps/powerpc/Makefile

@@ -61,11 +61,6 @@ ifeq ($(subdir),misc)
 sysdep_headers += sys/platform/ppc.h
 tests += test-gettimebase
 tests += tst-set_ppr
-
-# This test is expected to run and exit with EXIT_UNSUPPORTED on
-# processors that do not implement the Power ISA 2.06 or greater.
-# But the test makes use of instructions from Power ISA 2.06 and 2.07.
-CFLAGS-tst-set_ppr.c += -Wa,-many
 endif
 
 ifeq ($(subdir),wcsmbs)

sysdeps/powerpc/tst-set_ppr.c

@@ -44,7 +44,8 @@ get_thread_priority (void)
 {
   /* Read the PPR.  */
   ppr_t ppr;
-  asm volatile (MFPPR" %0" : "=r"(ppr));
+  asm volatile (".machine push; .machine power7; "MFPPR" %0; .machine pop"
+		: "=r"(ppr));
   /* Return the thread priority value.  */
   return EXTRACT_THREAD_PRIORITY (ppr);
 }