configure: Use -Wno-ignored-attributes if compiler warns about multiple aliases

configure: Use -Wno-ignored-attributes if compiler warns about multiple aliases

clang emits an warning when a double alias redirection is used, to warn
the the original symbol will be used even when weak definition is
overridden.  However, this is a common pattern for weak_alias, where
multiple alias are set to same symbol.

Reviewed-by: Fangrui Song <maskray@google.com>