Allow backslashes in FLEXLINK_FLAGS
Allow backslashes in FLEXLINK_FLAGS

Also in MKEXE, MKDLL and MKMAINDDLL as a result.

gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml