OvmfPkg: strip build paths in release builds

OvmfPkg: strip build paths in release builds

GenFw will embed a NB10 section which contains the path to the input file,
which means the output files have build paths embedded in them.  To reduce
information leakage and ensure reproducible builds, pass --zero in release
builds to remove this information.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3256
Signed-off-by: Ross Burton <ross.burton@arm.com>
Message-Id: <20210324115819.605436-1-ross.burton@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>