Fix MFS symbol redefinition with clang 3.8.0

Newest CLANG objcpy uses different name parsing.
Modify regexp to match (i.e. avoid substitution
of "/" or "-" with "_").

Obtained from: Semihalf
Sponsored by: Juniper Networks
Reviewed by: hselasky, zbb
Differential Revision: https://reviews.freebsd.org/D5873