Do not decorate MacOSX' -arch option with -Wl

Hi there,

I need to use the Maven NAR plugin to compile all kinds of stuff, including an executable that should only contain 32-bit code (i386 and ppc). The only way I could achieve this was by patching cpptasks-parallel after adding linker options '-arch i386 -arch ppc'.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>