different method signatures for mingw and visual c

[tesmai4]

I am writing code to be compiled with both MinGW and Visual C compiler. I am using define like this:

I have defined VISUAL_STUDIO In my project file as follows:

QMAKE_CFLAGS_DEBUG += -O2 VISUAL_STUDIO
                    QMAKE_CFLAGS += -O2 -DVISUAL_STUDIO

QMAKE_CFLAGS_DEBUG += -O2 VISUAL_STUDIO
                    QMAKE_CFLAGS += -O2 -DVISUAL_STUDIO

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I get multiple definition error for the following code

#ifdef VISUAL_STUDIO
int FUNCA(
#else
static inline int FUNCA(
#endif
    Pkt_t *pkt
    )

#ifdef VISUAL_STUDIO
int FUNCA(
#else
static inline int FUNCA(
#endif
    Pkt_t *pkt
    )

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Can anybody help me with this or any idea to do it in different was will be appreciated?