For osxppc, change size 8 to alignment 4.

You may need to delete and recompile some .o files!  This changes the
alignment of 8-byte values in C structs to match what Apple's gcc
does.  See Apple's "32-bit PowerPC Function Calling Conventions" at

    https://developer.apple.com
      /library/content/documentation/DeveloperTools/Conceptual/LowLevelABI
      /100-32-bit_PowerPC_Function_Calling_Conventions/32bitPowerPC.html

plat/osxppc/descr

@@ -10,10 +10,11 @@ var l={w}
 var la={w}
 var f={w}
 var fa={w}
+# Size 8 has alignment 4 in Mac OS, 8 in Linux.
 var d=8
-var da={d}
+var da=4
 var x=8
-var xa={x}
+var xa=4
 var ARCH=powerpc
 var PLATFORM=osxppc
 var PLATFORMDIR={EM}/share/ack/{PLATFORM}