HBSD: compile fix for archivers/snappy

compile fix:

c++: error: argument unused during compilation: '-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang' [-Werror,-Wunused-command-line-argument]
c++: error: argument unused during compilation: '-pie' [-Werror,-Wunused-command-line-argument]
ninja: build stopped: subcommand failed.

The use of 'USE_HARDENING= pie:off stackautoinit:off' did not work.

Signed-off-by: Loic loic.f@hardenedbsd.org