[LLD] [MinGW] Ignore the --no-seh flag

[mstorsjo]

Summary

The COFF linker automatically sets the IMAGE_DLL_CHARACTERISTICS_NO_SEH when suitable, similarly to link.exe.

(This description only is correct as long as D41252 is merged first, but I guess this change in itself could be merged independently.)

[rnk]

lgtm

I think LLD's current behavior will make things "just work" in as many cases as possible.

We could consider adding a warning when there were .sxdata sections present in the input, but no _load_config_used symbol was found. This indicates that there *were* structured exception handlers, but there was no load config to point to the safe SEH table.

MinGW/Options.td

 def build_id: F<"build-id">;
 def disable_auto_image_base: F<"disable-auto-image-base">;
 def enable_auto_image_base: F<"enable-auto-image-base">;
 def enable_auto_import: F<"enable-auto-import">;
 def full_shutdown: Flag<["--"], "full-shutdown">;
 def high_entropy_va: F<"high-entropy-va">, HelpText<"Enable 64-bit ASLR">;
 def major_image_version: S<"major-image-version">;
 def minor_image_version: S<"minor-image-version">;
+def no_seh: F<"no-seh">;
 def nxcompat: F<"nxcompat">, HelpText<"Enable data execution prevention">;
 def pic_executable: F<"pic-executable">;
 def sysroot: J<"sysroot">, HelpText<"Sysroot">;
 def tsaware: F<"tsaware">, HelpText<"Create Terminal Server aware executable">;
 def v: Flag<["-"], "v">, HelpText<"Display the version number">;
 def version: F<"version">, HelpText<"Display the version number and exit">;
 
 // Alias
 def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
 def alias_strip_s: Flag<["-"], "s">, Alias<strip_all>;