ruby: fix cross compiling extensions

Update pkgs/development/interpreters/ruby/default.nix

Co-authored-by: Artturi <Artturin@artturin.com>

pkgs/development/interpreters/ruby/default.nix

@@ -187,6 +187,18 @@ let
               sed -i '/CC_VERSION_MESSAGE/d' $rbConfig
             ''
           }
+
+          # Allow to override compiler. This is important for cross compiling as
+          # we need to set a compiler that is different from the build one.
+          awk -i inplace -F' = ' \
+            ' # operate on the line starting with
+              /^  CONFIG\["CC"\]/ {
+                # replace the right hand side
+                sub($2, "ENV[\"CC\"] || \"1\"")
+              }; { print }' "$rbConfig"
+          # test that the line isn't mangled in case upstream made the above unnecessary
+          grep -qx '  CONFIG\["CC"\] = ENV\["CC"\] || "1"' "$rbConfig"
+
           # Remove unnecessary external intermediate files created by gems
           extMakefiles=$(find $out/lib/ruby/gems -name Makefile)
           for makefile in $extMakefiles; do