Set a default machine type when using lld targeting Windows.

Fixes autotools checks parsing --help

pkgs/build-support/bintools-wrapper/add-lld-ldflags-before.sh

@@ -0,0 +1,6 @@
+# ld.lld has two incompatible command-line drivers: One for the gnu-compatible COFF linker and one for
+# the ELF linker. If no emulation is set (with -m), it will default to the ELF linker;
+# unfortunately, some configure scripts use `ld --help` to check for certain Windows-specific flags,
+# which don't show up in the help for the ELF linker. So we set a default -m here.
+
+extraBefore+=("-m" "@mtype@")

pkgs/build-support/bintools-wrapper/default.nix

@@ -384,6 +384,24 @@ stdenv.mkDerivation {
       ''
     )
 
+    ##
+    ## Set the default machine type so that $prefix-ld.lld uses the COFF driver for --help
+    ##
+    ## Needed because autotools parses --help for linker features...
+    ##
+    + optionalString (isLld && stdenv.targetPlatform.isWindows) (let
+      mtype =
+        /**/ if targetPlatform.isx86_32 then "i386pe"
+        else if targetPlatform.isx86_64 then "i386pep"
+        else if targetPlatform.isAarch32 then "thumb2pe"
+        else if targetPlatform.isAarch64 then "arm64pe"
+        else throw "unsupported target arch for lld";
+    in ''
+      export mtype=${mtype}
+      substituteAll ${./add-lld-ldflags-before.sh} add-local-ldflags-before.sh
+      cat add-local-ldflags-before.sh >> $out/nix-support/add-local-ldflags-before.sh
+    '')
+
     ##
     ## Code signing on Apple Silicon
     ##