CMake: revise how we deal with symbol export and static builds

- Remove the explicit PROJ_MSVC_DLL_IMPORT symbol used for importing
  symbols from a MSVC .dll: by default on MSVC, we use
  now __declspec(dllimport), unless PROJ_MSVC_DLL_EXPORT is defined
  by PROJ at build time. This makes it easier for users: they
  don't have to define anything special. This simplifies in particular
  the build of our binaries
- For static builds, export -DPROJ_DLL= as public, so that users
  that import PROJ through CMake mechanism don't have to do it
  manually.

1 files changed, 11 insertions, 9 deletions

diff --git a/src/proj.h b/src/proj.h
index 92515131..a09ae35c 100644
--- a/src/proj.h
+++ b/src/proj.h
@@ -140,15 +140,17 @@ extern "C" {
 /*! @cond Doxygen_Suppress */
 
 #ifndef PROJ_DLL
-#ifdef PROJ_MSVC_DLL_EXPORT
-#define PROJ_DLL __declspec(dllexport)
-#elif defined(PROJ_MSVC_DLL_IMPORT)
-#define PROJ_DLL __declspec(dllimport)
-#elif defined(__GNUC__)
-#define PROJ_DLL __attribute__ ((visibility("default")))
-#else
-#define PROJ_DLL
-#endif
+#  if defined(_MSC_VER)
+#    ifdef PROJ_MSVC_DLL_EXPORT
+#      define PROJ_DLL __declspec(dllexport)
+#    else
+#      define PROJ_DLL __declspec(dllimport)
+#    endif
+#  elif defined(__GNUC__)
+#    define PROJ_DLL __attribute__ ((visibility("default")))
+#  else
+#    define PROJ_DLL
+#  endif
 #endif
 
 #ifdef PROJ_SUPPRESS_DEPRECATION_MESSAGE