GDNative: Fix symbols visibility for GCC

[o01eg]

I'm building native library with CMake and found out default visibility settings make it unusable with Godot because symbols are hidden.
This PR makes exported functions visible when compiling them with GCC.

Copy of godotengine/godot-headers#81

[o01eg]

Are there any news regarding this PR?

[touilleMan]

Would it be useful to add something similar to the GDAPI macro ? I guess it depends on the flags used when compiling Godot but from what I understand it could help with final binary size
Not sure why, but currently only iOS use the custom visibility attribute:

godot/modules/gdnative/include/gdnative/gdnative.h

Lines 38 to 53 in 51d6891

	#if defined(_WIN32) || defined(__ANDROID__)
	#define GDCALLINGCONV
	#define GDAPI GDCALLINGCONV
	#elif defined(__APPLE__)
	#include "TargetConditionals.h"
	#if TARGET_OS_IPHONE
	#define GDCALLINGCONV __attribute__((visibility("default")))
	#define GDAPI GDCALLINGCONV
	#elif TARGET_OS_MAC
	#define GDCALLINGCONV __attribute__((sysv_abi))
	#define GDAPI GDCALLINGCONV
	#endif
	#else // !_WIN32 && !__APPLE__
	#define GDCALLINGCONV __attribute__((sysv_abi))
	#define GDAPI GDCALLINGCONV
	#endif

[BastiaanOlij]

Would it be useful to add something similar to the GDAPI macro ? I guess it depends on the flags used when compiling Godot but from what I understand it could help with final binary size
Not sure why, but currently only iOS use the custom visibility attribute:

I could be completely wrong but that may be a left over from earlier times, don't we statically link GDNative modules in iOS? Or has that changed since I last used GDNative in iOS

[BastiaanOlij]

I don't use GCC myself so i can't test it but this change seems sound. Functions marked as GDN_EXPORT need to be set to visible so if GCC does not do so by default then this seems like the right way to fix it to me.

[akien-mga]

I could be completely wrong but that may be a left over from earlier times, don't we statically link GDNative modules in iOS? Or has that changed since I last used GDNative in iOS

There's now proper support for dynamically linking GDNative on iOS, implemented by @naithar: #39996.

[BastiaanOlij]

There's now proper support for dynamically linking GDNative on iOS, implemented by @naithar: #39996.

That is cool! Unrelated to this PR really though :)

[akien-mga]

Thanks!

[o01eg]

Could it be backported to 3.2?

[akien-mga]

Yes, that's what the cherrypick:3.2 label means.

[akien-mga]

Cherry-picked for 3.2.4.