After 1af25a986069f2ae8c724133fa8649bb795a7925, we stop unconditionally
retaining wrapped symbols, which means that LTO's summary-based global
dead stripping can eliminate them even if they'll be referenced by a
linker script after the wrapping is performed. Mark symbols referenced
in linker scripts as referenced in addition to isUsedInRegularObj in
order for the wrapping logic to correctly set referencedAfterWrap and
prevent LTO from eliminating them.
An alternative would have been to change the referencedAfterWrap logic
to look at isUsedInRegularObj in addition to referenced, but
isUsedInRegularObj is also set in other places (e.g. for the entry
symbol), and it's not clear that we want referencedAfterWrap to take
all those places into account, so it seemed better to keep that logic
as-is and instead set referenced for linker script-referenced symbols.