rust: make linking on wasi32 work

Rust assumes the linker is lld-flavored (unless it's named clang),
and passes arguments accordingly. Two things are required to make that
work:

* Set the linker to ld.lld
* disable linker hardening flags (they'd be passed befor the -flavor
  arg, breakin that, on top of having no effect)

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

@@ -334,7 +334,7 @@ stdenvNoCC.mkDerivation {
       hardening_unsupported_flags+=" pic"
     ''
 
-    + optionalString (targetPlatform.isAvr || targetPlatform.isWindows) ''
+    + optionalString (targetPlatform.isAvr || targetPlatform.isWindows || targetPlatform.isWasi) ''
       hardening_unsupported_flags+=" relro bindnow"
     ''
 

pkgs/build-support/rust/lib/default.nix

@@ -23,8 +23,10 @@ rec {
 
     ccForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc";
     cxxForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}c++";
-    linkerForHost = if shouldUseLLD stdenv.targetPlatform
-      && !stdenv.cc.bintools.isLLVM
+    # For wasi: Rust recognizes "clang" or "gcc" as compilers, but not "cc" as in ccForHost.
+    #           So it defaults to expecting lld and passes arguments accordingly.
+    linkerForHost = if stdenv.targetPlatform.isWasi
+      || (shouldUseLLD stdenv.targetPlatform && !stdenv.cc.bintools.isLLVM)
       then "${pkgsBuildHost.llvmPackages.bintools}/bin/${stdenv.cc.targetPrefix}ld.lld"
       else ccForHost;