Allow disabling either the full auto import feature, or just forbidding the cases that require runtime fixups.
As long as all auto imported variables are referenced from separate .refptr$<name> sections, we can alias them on top of the IAT entries and don't actually need any runtime fixups via pseudo relocations. LLVM generates references to variables in .refptr stubs, if it isn't known that the variable for sure is defined in the same object module. Runtime pseudo relocs are needed if the addresses of auto imported variables are used in constant initializers though.
Fixing up runtime pseudo relocations requires the use of VirtualProtect (which is disallowed in WinStore/UWP apps) or VirtualProtectFromApp. To allow any risk of ambiguity, allow rejecting cases that would require this at the linker stage.
This adds support for the --disable-runtime-pseudo-reloc and --disable-auto-import options in the MinGW driver (matching GNU ld.bfd) with corresponding lld private options in the COFF driver.