build: use CMake to propagate CMARK_STATIC_DEFINE

The `CMARK_STATIC_DEFINE` macro identifies that the library is being
linked statically, which is important information for building on
Windows. This uses CMake to automatically propagate the necessary
definition to the users and the build of the library itself rather than
having everyone specify it manually.

src/CMakeLists.txt

@@ -55,9 +55,6 @@ set_target_properties(${PROGRAM} PROPERTIES
 
 if (CMARK_STATIC)
   target_link_libraries(${PROGRAM} ${STATICLIBRARY})
-  # Disable the PUBLIC declarations when compiling the executable:
-  set_target_properties(${PROGRAM} PROPERTIES
-    COMPILE_FLAGS -DCMARK_STATIC_DEFINE)
 elseif (CMARK_SHARED)
   target_link_libraries(${PROGRAM} ${LIBRARY})
 endif()
@@ -92,8 +89,9 @@ endif()
 if (CMARK_STATIC)
   add_library(${STATICLIBRARY} STATIC ${LIBRARY_SOURCES})
   cmark_add_compile_options(${STATICLIBRARY})
+  target_compile_definitions(${STATICLIBRARY} PUBLIC
+    CMARK_STATIC_DEFINE)
   set_target_properties(${STATICLIBRARY} PROPERTIES
-    COMPILE_FLAGS -DCMARK_STATIC_DEFINE
     POSITION_INDEPENDENT_CODE ON
     VERSION ${PROJECT_VERSION})
   if(MSVC)