Use config file template instead of Rakefile template
diff --git a/templates/build_config.rb.template b/templates/build_config.rb.template
new file mode 100644
index 0000000..4cb4810
--- /dev/null
+++ b/templates/build_config.rb.template
@@ -0,0 +1,5 @@
+%YAML 1.2
+--- |
+  module GrpcBuildConfig
+    CORE_WINDOWS_DLL = '/tmp/libs/opt/grpc-${settings.core_version.major}.dll'
+  end
\ No newline at end of file