Use "gcc --print-multiarch" to determine directory names for library installs

Use "gcc --print-multiarch" to determine directory names for library installs

Previously, we had hardcoded names of lib32 and lib64. Instead, we now
ask gcc for the actual triple being targeted, (such as, for example,
lib/i386-linux-gnu or lib/x86_64-linux-gnu).

Using these correct names means that the user of Glaze can put a
literal $LIB into LD_PRELOAD or LD_LIBRARY_PATH and the run-time
linker will expand that to the correct name based on the architecture
of the program being linked