How to use CGO for header file with conditionally inline function?

Question

I´m currently writing a Go wrapper for C api which contains header with this ifdef:

#ifdef  __cplusplus
#define TEST_INLINE inline
#else
#define TEST_INLINE 
#endif

TEST_INLINE int callC_inline (){
    return 1;
}

Unfortunately, I cannot change header since it's a third-party code. The code compiles fine if I pass -Wl,--allow-multiple-definition to linker, but I think it's a bad practice. So, I'm interested is there any flag I can pass to CGO or trick to satisfy #ifdef __cplusplus condition?

Compilation exception:

C:\Temp\go-build318595762\cgo_issue\_obj\lib.o: In function `callC_inline':
./lib.h:11: multiple definition of `callC_inline'
C:\Temp\go-build318595762\cgo_issue\_obj\main.cgo2.o:D:/work/go/cgo_issue/lib.h:11: first defined here
collect2.exe: error: ld returned 1 exit status

main.go:

package main

//#cgo CFLAGS: -std=gnu99
//#include "lib.h"
import "C"
import "fmt"

func main() {
    fmt.Printf("Go call\n")
    C.callC()
}

lib.h:

void callC();

#ifdef  __cplusplus
#define TEST_INLINE inline
#else
#define TEST_INLINE 
#endif

TEST_INLINE int callC_inline (){
    return 1;
}

lib.c:

#include "lib.h"
#include  <stdio.h>

void callC(){
    printf("C call\n");
}

Answer 1

It is possible to pass some additional info to cgo via special comments. In this case // #cgo CFLAGS: -D__cplusplus

More info here