bcache-tools: Fix the cross compilation

Fix #90726.

pkgs/tools/filesystems/bcache-tools/default.nix

@@ -20,6 +20,7 @@ stdenv.mkDerivation rec {
     sed -e "/INSTALL.*initramfs\/hook/d" \
         -e "/INSTALL.*initcpio\/install/d" \
         -e "/INSTALL.*dracut\/module-setup.sh/d" \
+        -e "s/pkg-config/$PKG_CONFIG/" \
         -i Makefile
   '';
 
@@ -28,8 +29,12 @@ stdenv.mkDerivation rec {
     ./fix-static.patch
   ];
 
+  makeFlags = [
+    "PREFIX=${placeholder "out"}"
+    "UDEVLIBDIR=${placeholder "out"}/lib/udev/"
+  ];
+
   preBuild = ''
-    export makeFlags="$makeFlags PREFIX=\"$out\" UDEVLIBDIR=\"$out/lib/udev/\"";
     sed -e "s|/bin/sh|${bash}/bin/sh|" -i *.rules
   '';