CMake: define digidocpp_EXPORTS on digidocpp target for static builds

When BUILD_SHARED_LIBS=OFF on Windows, CMake does not automatically
define digidocpp_EXPORTS on the digidocpp target (it only does this for
shared libraries). This causes DIGIDOCPP_EXPORT in Exports.h to resolve
to __declspec(dllimport) instead of __declspec(dllexport), which is
incorrect when compiling the library itself.

Apply the same pattern already used for digidocpp_util and digidocpp_tsl
at line 83-84: set COMPILE_DEFINITIONS digidocpp_EXPORTS on the target
for static builds.

Author: lnagel

src/CMakeLists.txt

@@ -257,6 +257,7 @@ endif()
 
 if(NOT ${BUILD_SHARED_LIBS})
     set(STATIC_TARGETS minizip digidocpp_tsl digidocpp_util)
+    set_property(TARGET digidocpp PROPERTY COMPILE_DEFINITIONS digidocpp_EXPORTS)
 endif()
 
 install(TARGETS digidocpp ${STATIC_TARGETS}