Avoid $LDFLAGS being nil when building locally
Avoid $LDFLAGS being nil when building locally

Ruby 2.0 mkmf uses $LDFLAGS in several places and being set as nil is bad
if previously it had a correct value.

alexdowad/sqlite3-ruby,AutogrowSystems/sqlite3-ruby,alexdowad/sqlite3-ruby,AutogrowSystems/sqlite3-ruby,duhlin/sqlite3-ruby,duhlin/sqlite3-ruby