Fix some leftover binaries and shared libraries in the system that still

Fix some leftover binaries and shared libraries in the system that still
have an executable stack, due to linking in hand-assembled .S or .s
files, that have no .GNU-stack sections:

RWX --- ---  /lib/libcrypto.so.6
RWX --- ---  /lib/libmd.so.5
RWX --- ---  /lib/libz.so.6
RWX --- ---  /lib/libzpool.so.2
RWX --- ---  /usr/lib/liblzma.so.5

These were found using scanelf, from the sysutils/pax-utils port.

Reviewed by:	kib