cgo: full supports cgo preambles and auto compile c files

_demo/cgocfiles/cgocfiles.go

@@ -6,12 +6,6 @@ package main
 import "C"
 import "fmt"
 
-// TODO(lijie): workaround for c files compiling
-const (
-	LLGoFiles   = "in.c"
-	LLGoPackage = "link"
-)
-
 func main() {
 	r := C.test_structs(&C.s4{a: 1}, &C.s8{a: 1, b: 2}, &C.s12{a: 1, b: 2, c: 3}, &C.s16{a: 1, b: 2, c: 3, d: 4}, &C.s20{a: 1, b: 2, c: 3, d: 4, e: 5})
 	fmt.Println(r)