CoreFoundation: use modern standards for DLL build

Use the CMake defined `_EXPORT` macro to determine if the symbols should
be exported.  Rely on `_USRDLL` to indicate if the compilation is meant
for static or shared builds and mark the symbols for export or not to
prevent the symbols from being re-exported from the consuming library.

Author: compnerd

CMakeLists.txt

@@ -34,8 +34,11 @@ ExternalProject_Add(CoreFoundation
                       ${CMAKE_COMMAND}
                     CMAKE_ARGS
                       -DBUILD_SHARED_LIBS=NO
-                      -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
                       -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+                      -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+                      # NOTE(compnerd) ensure that we build it as a DLL as we
+                      # wish to re-export the symbols from Foundation
+                      -DCMAKE_C_FLAGS="${CMAKE_C_FLAGS} -D_USRDLL"
                       -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
                       -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
                       -DCMAKE_INSTALL_LIBDIR=usr/lib

CoreFoundation/Base.subproj/CFBase.h

@@ -127,16 +127,20 @@
 #endif
 
 #if TARGET_OS_WIN32
-    #if !defined(CF_EXPORT)
-        #if defined(CF_BUILDING_CF) && defined(__cplusplus)
-            #define CF_EXPORT extern "C" __declspec(dllexport)
-        #elif defined(CF_BUILDING_CF) && !defined(__cplusplus)
-            #define CF_EXPORT extern __declspec(dllexport)
-        #elif defined(__cplusplus)
-            #define CF_EXPORT extern "C" __declspec(dllimport)
+    #if defined(__cplusplus)
+        #define _CF_EXTERN extern "C"
+    #else
+        #define _CF_EXTERN extern
+    #endif
+
+    #if defined(_USRDLL)
+        #if defined(CoreFoundation_EXPORTS)
+            #define CF_EXPORT _CF_EXTERN __declspec(dllexport)
         #else
-            #define CF_EXPORT extern __declspec(dllimport)
+            #define CF_EXPORT _CF_EXTERN __declspec(dllimport)
         #endif
+    #else
+        #define CF_EXPORT _CF_EXTERN
     #endif
 #else
 #define CF_EXPORT extern

CoreFoundation/CMakeLists.txt

@@ -329,6 +329,11 @@ elseif(CMAKE_SYSTEM_NAME STREQUAL Windows)
   target_compile_definitions(CoreFoundation
                              PRIVATE
                                -DDEPLOYMENT_TARGET_WINDOWS)
+  if(BUILD_SHARED_LIBS)
+    target_compile_definitions(CoreFoundation
+                               PRIVATE
+                                 -D_USRDLL)
+  endif()
 endif()
 target_compile_definitions(CoreFoundation
                            PRIVATE