Fix bignum asm for OS X PPC

A typical PPC-supporting Xcode toolchain (Apple gcc + Apple cctools
assembler), when targeting PPC, treats semicolons as comment
delimiters, even for inline assembly. As a result, commit
02d800c15160b1e8dc26e405e41c1ae91d38dcd2 broke the bignum asm code
for OS X on both PPC32 and PPC64, by effectively commenting out
nearly all of the asm code. Replacing the semicolons with \n makes
this code work again.