Solaris: Support -i in shlib-build

Solaris: Support -i in shlib-build

Our librokenafs.map file contains symbols that we may not actually
define, since the list of exported symbols varies depending on the
platform's capabilities. This causes errors during linking, which can
be suppressed by marking all symbols as "= EXTERN". Do so by having
shlib-build modify the mapfile at link-time, when -i is specified to
indicate ignoring undefined symbols.

Change-Id: I043fca6c8206a19fb7bddbc8e624baeaaff3ab00
Reviewed-on: http://gerrit.openafs.org/3365
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>