blitz: Remove hardcoded LIBPATH additions

These make assumptions which cause the path to be set
incorrectly in several situations, causing the build
to fail.  Example: On 64-bit Windows, the 32-bit
libraries can still be used, causing linker errors.
lib64 is also an incorrect assumption for many Linux
systems which don't use biarch paths.
Merge pull request #1164 from rleigh-dundee/cpp-libpath

blitz: Remove hardcoded LIBPATH additions