powerpc: Work around gcc's -fno-omit-frame-pointer bug

This bug is causing random crashes
(http://bugzilla.kernel.org/show_bug.cgi?id=11414).

-fno-omit-frame-pointer is only needed on powerpc when -pg is also
supplied, and there is a gcc bug that causes incorrect code generation
on 32-bit powerpc when -fno-omit-frame-pointer is used---it uses stack
locations below the stack pointer, which is not allowed by the ABI
because those locations can and sometimes do get corrupted by an
interrupt.

This ensures that CONFIG_FRAME_POINTER is only selected by ftrace.
When CONFIG_FTRACE is enabled we also pass -mno-sched-epilog to work
around the gcc codegen bug.

Patch based on work by:
	Andreas Schwab <schwab@suse.de>
	Segher Boessenkool <segher@kernel.crashing.org>

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/powermac/Makefile

@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FTRACE
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg
+CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
 endif
 
 obj-y				+= pic.o setup.o time.o feature.o pci.o \