Fix LD_PRELOAD error on Linux.

On 64-bit Linux systems, if LD_PRELOAD isn't a relative/absolute
pathname to libswmhack.so, then ld.so attempts to load a 32-bit version
for 32-bit programs.  This produces an error message.  The solution is
to either build and install a 32-bit libswmhack.so.0.0 or use an
absolute/relative path so that ld.so only loads libswmhack.so for 64-bit
binaries.

Fix Makefiles to set variables before they are referenced.