added optional static linking on linux

CMakeLists.txt

@@ -12,10 +12,9 @@ file(GLOB_RECURSE HEADER_FILES "*.hh" "*.h" "*.hpp" "*.inl")
 add_subdirectory(contrib/zlib)
 add_subdirectory(contrib/irrXML)
 
+set(ASSIMP_LINK_TYPE SHARED CACHE String "link type for assimp")
 if(MSVC)
-    set(ASSIMP_LINK_TYPE STATIC)
-else()
-    set(ASSIMP_LINK_TYPE SHARED)
+    set(ASSIMP_LINK_TYPE STATIC CACHE String "" FORCE)
 endif()
 
 add_library(assimp ${ASSIMP_LINK_TYPE} ${SOURCE_FILES} ${HEADER_FILES})