wasilibc: use .imports file for lld

instead of passing in the --allow-undefined-file, we can just let lld
find the file.

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

@@ -301,8 +301,6 @@ stdenv.mkDerivation {
 
     + optionalString targetPlatform.isWasm ''
       hardening_unsupported_flags+=" stackprotector fortify pie pic"
-    '' + optionalString (targetPlatform.isWasm && libc != null) ''
-      echo "--allow-undefined-file=${libc}/share/wasm32-wasi/undefined-symbols.txt" >> $out/nix-support/cc-ldflags
     ''
 
     + optionalString (libc != null && targetPlatform.isAvr) ''

pkgs/development/libraries/wasilibc/default.nix

@@ -17,6 +17,7 @@ stdenv.mkDerivation {
 
   postInstall = ''
     mv $out/lib/*/* $out/lib
+    ln -s $out/share/wasm32-wasi/undefined-symbols.txt $out/lib/wasi.imports
   '';
 
   meta = {