build.info: Make it possible to have more than one item in KEYWORD[]

build.info: Make it possible to have more than one item in KEYWORD[]

So far, the "index" part of KEYWORD[whatever] could only handle one
item.  There are cases, however, where we want to add the exact same
value to multiple items.  This is especially helpful if a variable
that may have multi-item values are used in the "index" part.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11185)