compiler: fix debug metadata

Not setting the correct debug location at function entry leads to
instructions getting the address of the previously emitted function,
which is of course wrong. LLVM complains about it when validating a
module.

compiler.go

@@ -1103,6 +1103,11 @@ func (c *Compiler) parseFunc(frame *Frame) error {
 		frame.fn.llvmFn.SetLinkage(llvm.InternalLinkage)
 	}
 
+	if c.debug {
+		pos := c.ir.program.Fset.Position(frame.fn.fn.Pos())
+		c.builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), frame.difunc, llvm.Metadata{})
+	}
+
 	// Pre-create all basic blocks in the function.
 	for _, block := range frame.fn.fn.DomPreorder() {
 		llvmBlock := c.ctx.AddBasicBlock(frame.fn.llvmFn, block.Comment)