Change OSL_RSOP to properly export symbol linkage

Signed-off-by: Larry Gritz <[email protected]>

src/include/OSL/rs_free_function.h

@@ -31,7 +31,7 @@ extern "C" {
 
 // Prefix for OSL shade op declarations.
 // "C" linkage (no C++ name mangling) and local visibility
-#define OSL_RSOP extern "C"
+#define OSL_RSOP OSLEXECPUBLIC extern "C"
 
 // We are choosing to use unique names encoding parameters directly
 // as opposed to using overloaded functions.