consolidate cmake documentation flow

CMakeLists.txt

@@ -168,13 +168,6 @@ option(OPENMW_USE_SYSTEM_GOOGLETEST "Use system Google Test library." OFF)
 option(OPENMW_UNITY_BUILD "Use fewer compilation units to speed up compile time" FALSE)
 option(OPENMW_LTO_BUILD "Build OpenMW with Link-Time Optimization (Needs ~2GB of RAM)" OFF)
 
-# what is necessary to build documentation
-IF( BUILD_DOCS )
-    # Builds the documentation.
-    FIND_PACKAGE( Sphinx REQUIRED )
-    FIND_PACKAGE( Doxygen REQUIRED )
-ENDIF()
-
 # OS X deployment
 option(OPENMW_OSX_DEPLOYMENT OFF)
 
@@ -1107,11 +1100,16 @@ elseif(NOT APPLE)
     endif(WIN32)
 endif(OPENMW_OSX_DEPLOYMENT AND APPLE)
 
+# what is necessary to build documentation
+if ( BUILD_DOCS )
+    # Builds the documentation.
+    FIND_PACKAGE( Sphinx REQUIRED )
+    FIND_PACKAGE( Doxygen REQUIRED )
+
     # Doxygen Target -- simply run 'make doc' or 'make doc_pages'
     # output directory for 'make doc'       is "${OpenMW_BINARY_DIR}/docs/Doxygen"
     # output directory for 'make doc_pages' is "${DOXYGEN_PAGES_OUTPUT_DIR}" if defined
     #                                       or "${OpenMW_BINARY_DIR}/docs/Pages" otherwise
-find_package(Doxygen)
     if ( DOXYGEN_FOUND )
         # determine output directory for doc_pages
         if (NOT DEFINED DOXYGEN_PAGES_OUTPUT_DIR)
@@ -1129,6 +1127,7 @@ if (DOXYGEN_FOUND)
             WORKING_DIRECTORY ${OpenMW_BINARY_DIR}
             COMMENT "Generating documentation for the github-pages at ${DOXYGEN_PAGES_OUTPUT_DIR}" VERBATIM)
     endif ()
+endif()
 
 # Qt localization
 if (USE_QT)