[LLVM-C] Add GetFunctionType Method

[wsmoses]

Summary

This adds a get functiontype from function method to the LLVM C ABI. This is required to support opaque pointers.

[nikic]

This is already provided in a more general way by LLVMGlobalGetValueType.

[wsmoses]

You are absolutely correct, did not find that one.

llvm/include/llvm-c/Core.h

  * @see llvm::Function::setCallingConv()
  *
  * @param Fn Function to operate on
  * @param CC LLVMCallConv to set calling convention to
  */
 void LLVMSetFunctionCallConv(LLVMValueRef Fn, unsigned CC);
 
 /**
+ * Obtain the function type of a function.
+ *
+ * @see llvm::Function::getFunctionType()
+ */
+unsigned LLVMGetFunctionType(LLVMValueRef Fn);
+
+/**
  * Obtain the name of the garbage collector to use during code
  * generation.
  *
  * @see llvm::Function::getGC()
  */
 const char *LLVMGetGC(LLVMValueRef Fn);
 
 /**

llvm/lib/IR/Core.cpp

unsigned LLVMGetFunctionCallConv(LLVMValueRef Fn) {
   return unwrap<Function>(Fn)->getCallingConv();
 }
 
 void LLVMSetFunctionCallConv(LLVMValueRef Fn, unsigned CC) {
   return unwrap<Function>(Fn)->setCallingConv(
     static_cast<CallingConv::ID>(CC));
 }
 
+LLVMTypeRef LLVMGetFunctionType(LLVMValueRef Fn) {
+  return wrap(unwrap<Function>(Fn)->getFunctionType());
+}
+
 const char *LLVMGetGC(LLVMValueRef Fn) {
   Function *F = unwrap<Function>(Fn);
   return F->hasGC()? F->getGC().c_str() : nullptr;
 }
 
 void LLVMSetGC(LLVMValueRef Fn, const char *GC) {
   Function *F = unwrap<Function>(Fn);
   if (GC)