gcc: move cygwin DLLs to $target/bin

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

@@ -603,7 +603,7 @@ stdenvNoCC.mkDerivation {
       installPhase =
         if targetPlatform.isCygwin then
           ''
-            echo addToSearchPath "HOST_PATH" "${cc_bin}/lib" >> $out
+            echo addToSearchPath "HOST_PATH" "${cc_solib}/bin" >> $out
             # Work around build failure caused by the gnulib workaround for
             # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114870. remove after
             # gnulib is updated in core packages (e.g. iconv, gnupatch, gnugrep)

pkgs/development/compilers/gcc/common/builder.nix

@@ -363,6 +363,13 @@ originalAttrs:
           fi
       done
     ''
+    + lib.optionalString stdenv.targetPlatform.isCygwin ''
+      targetBinDir="''${targetConfig+$targetConfig/}bin"
+      for i in "''${!outputBin}/$targetLibDir"/cyg*.dll; do
+        mkdir -p "''${!outputLib}/$targetBinDir"
+        mv "$i" "''${!outputLib}/$targetBinDir"/
+      done
+    ''
     # if cross-compiling, link from $lib/lib to $lib/${targetConfig}.
     # since native-compiles have $lib/lib as a directory (not a
     # symlink), this ensures that in every case we can assume that