[cmake] Fix previous mistake CMAKE_EXPORT to FALSE when python only.

CMakeLists.txt

@@ -8,14 +8,14 @@ SET(PROJECT_NAME sot-core)
 SET(PROJECT_DESCRIPTION "Hierarchical task solver plug-in for dynamic-graph.")
 SET(PROJECT_URL "http://github.com/${PROJECT_ORG}/${PROJECT_NAME}")
 
-# Export CMake Target
-SET(PROJECT_USE_CMAKE_EXPORT TRUE)
-
-# Disable -Werror on Unix for now.
 IF (NOT INSTALL_PYTHON_INTERFACE_ONLY)
-  SET(CXX_DISABLE_WERROR True)
+  # Export CMake Target
+  SET(PROJECT_USE_CMAKE_EXPORT TRUE)
 ENDIF(NOT INSTALL_PYTHON_INTERFACE_ONLY)
 
+# Disable -Werror on Unix for now.
+SET(CXX_DISABLE_WERROR True)
+
 INCLUDE(cmake/base.cmake)
 
 # Specify the project.