VMS build file template: assign 'arch' to local symbol table

VMS build file template: assign 'arch' to local symbol table

Since the local symbol table is looked up before the global symbol
table, 'arch' assigned in the local symbol table of the DCL where MMS
is called would be seen before the 'arch' defined in descrip.mms.
Assigning it to the local symbol table in descrip.mms removes that
issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1853)
(cherry picked from commit 3ee24d4acaff1c247db89c5cfcac17749dc3d7bc)