ld,dlltool: move read-only delayimp data into .rdata

This allows the delay IAT to be in its own section with nothing else, as
required by IMAGE_GUARD_DELAYLOAD_IAT_IN_ITS_OWN_SECTION, documented at
https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#load-configuration-layout

Signed-off-by: Jeremy Drake <sourceware-bugzilla@jdrake.com>