libobs,obs-outputs: Fix librtmp1 interference

Details in #6226, basically this fixes an issue where OBS links
to the system-installed librtmp1, which is incompatible with our
librtmp.

Co-authored-by: ewhac <[email protected]>

libobs/util/c99defs.h

@@ -50,7 +50,7 @@
 #ifdef _MSC_VER
 #define EXPORT __declspec(dllexport)
 #else
-#define EXPORT
+#define EXPORT __attribute__((visibility("default")))
 #endif
 
 #include <stddef.h>

plugins/obs-outputs/CMakeLists.txt

@@ -96,9 +96,11 @@ if(ENABLE_RTMPS STREQUAL "AUTO" OR ENABLE_RTMPS STREQUAL "ON")
       target_link_libraries(obs-outputs PRIVATE ${FOUNDATION_FRAMEWORK}
                                                 ${SECURITY_FRAMEWORK})
       set_target_properties(obs-outputs PROPERTIES CXX_VISIBILITY_PRESET hidden)
+      set_target_properties(obs-outputs PROPERTIES C_VISIBILITY_PRESET hidden)
 
     elseif(OS_POSIX)
       set_target_properties(obs-outputs PROPERTIES CXX_VISIBILITY_PRESET hidden)
+      set_target_properties(obs-outputs PROPERTIES C_VISIBILITY_PRESET hidden)
     endif()
   endif()
 else()