Enable top and make other tweaks in plat/osxppc/descr

David Given made top for PowerPC.  Copy the asopt phase (running top)
from linuxppc to osxppc.

Remove CC_ALIGN=-Vr to become compatible with Apple's gcc.  Apple uses
left adjustment for bitfields; the first bitfield is on the left side
(the big end), not the right side.

Remove unused variables C_LIB and OLD_C_LIB; the file libc-ansi.a
doesn't exist.

Change MACHOPT_F from -m10 to -m3.  This means to use no more than 3
adds and shifts to optimize a multiply by a constant.  I pick -m3
because -m4 can use too many instructions.  At -m4, the compiler
rewrites

    n * 14

as

    s = n << 1
    (s << 3) + (0 - s)

This means (n * 16 - n * 2), but even at ack -O6, the compiler doesn't
rewrite (a + (0 - b)) as (a - b).  The compiler emits 5 instructions:
2 of rlinmw for 2 left shifts, then addi to load 0 in a register, subf
to subtract from that 0, then add.  These 5 instructions cost 5 cycles
on the MPC7450, using the cycle counts from mach/powerpc/ncg/table.

At -m3, (n * 14) becomes 2 instructions: addi to load 14 in a register
and mullw to multiply.  This also costs 5 cycles (because mullw costs
4 cycles), but uses less space.

plat/osxppc/descr

@@ -19,12 +19,7 @@ var PLATFORM=osxppc
 var PLATFORMDIR={EM}/share/ack/{PLATFORM}
 var CPP_F=-D__unix
 var ALIGN=-a0:4 -a1:4 -a2:4096 -a3:4 -b0:0x129c
-var C_LIB={PLATFORMDIR}/libc-ansi.a
-# bitfields reversed for compatibility with (g)cc.
-# XXX this is from linux386, might be wrong for osxppc
-var CC_ALIGN=-Vr
-var OLD_C_LIB={C_LIB}
-var MACHOPT_F=-m10
+var MACHOPT_F=-m3
 # var EGO_PLAT_FLAGS=-M{EM}/share/ack/ego/{ARCH}.descr
 
 # Override the setting in fe so that files compiled for osxppc can see
@@ -41,6 +36,15 @@ name be
 	stdout
 	need .e
 end
+name asopt
+	from .s
+	to .so
+	program {EM}/lib/ack/linuxppc/top
+	args
+	optimizer
+	stdin
+	stdout
+end
 name as
 	from .s.so
 	to .o