Use GNU visibility attributes when on non-Windows.

This reduces binary sizes by several megabytes on my system.

CMakeLists.txt

@@ -188,7 +188,7 @@ if(MSVC)
 # Otherwise, we're not using Visual Studio
 else()
   # Set the compile flags to have all warnings on (including shadowed variables)
-  set(CXXFLAGS "${CXXFLAGS} -Wall -Wextra -Wpedantic -Wno-unused-parameter ${CMAKE_CXX_FLAGS}")
+  set(CXXFLAGS "${CXXFLAGS} -fvisibility=hidden -fvisibility-inlines-hidden -Wall -Wextra -Wpedantic -Wno-unused-parameter ${CMAKE_CXX_FLAGS}")
   # Also, if we are building under MinGW, add another define for MinGW
   if(MINGW)
     add_definitions(-DMINGW)

include/services.h

@@ -51,8 +51,8 @@
 #define _(x) x
 
 #ifndef _WIN32
-# define DllExport
-# define CoreExport
+# define DllExport __attribute__ ((visibility ("default")))
+# define CoreExport __attribute__ ((visibility ("default")))
 # define anope_close close
 #else
 # include "anope_windows.h"