backend/build: add hack to workaround missing interop features

backend.native/LlvmHacks.h

@@ -0,0 +1,9 @@
+typedef int32_t LLVMAttributeSet;
+
+// Return value type of LLVMGetFunctionAttr is enum LLVMAttribute;
+// it is not a strict enum, but used as a set of enum values instead.
+// Currently it is not possible to configure interop to treat a enum in such way,
+// so redeclare the function with appropriate return value type:
+static inline LLVMAttributeSet LLVMGetFunctionAttrSet(LLVMValueRef Fn) {
+    return LLVMGetFunctionAttr(Fn);
+}

backend.native/build.gradle

@@ -134,6 +134,7 @@ List<String> llvmLinkerOpts() {
 kotlinNativeInterop {
    llvm {
      defFile 'llvm.def'
+     headers files('LlvmHacks.h')
      compilerOpts "-fPIC", "-I$llvmDir/include"
      linkerOpts llvmLinkerOpts()
    }