SIP < 4.10 has no -o option, therefore causing builds to fail
http://hub.qgis.org/issues/5944

diff -Nur qgis-1.8.0/python/CMakeLists.txt qgis-1.8.0-sip410/python/CMakeLists.txt
--- qgis-1.8.0/python/CMakeLists.txt	2012-06-12 21:28:18.000000000 +0200
+++ qgis-1.8.0-sip410/python/CMakeLists.txt	2012-07-04 22:21:08.531677519 +0200
@@ -62,7 +62,7 @@
 # core module
 FILE(GLOB sip_files_core core/*.sip)
 SET(SIP_EXTRA_FILES_DEPEND ${sip_files_core})
-SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -o -a ${CMAKE_BINARY_DIR}/python/qgis.core.api)
+SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -a ${CMAKE_BINARY_DIR}/python/qgis.core.api)
 ADD_SIP_PYTHON_MODULE(qgis.core core/core.sip qgis_core)
 
 # additional gui includes
@@ -77,7 +77,7 @@
 # gui module
 FILE(GLOB sip_files_gui gui/*.sip)
 SET(SIP_EXTRA_FILES_DEPEND ${sip_files_core} ${sip_files_gui})
-SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -o -a ${CMAKE_BINARY_DIR}/python/qgis.gui.api)
+SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -a ${CMAKE_BINARY_DIR}/python/qgis.gui.api)
 ADD_SIP_PYTHON_MODULE(qgis.gui gui/gui.sip qgis_core qgis_gui)
 
 # additional analysis includes
@@ -91,13 +91,13 @@
 # analysis module
 FILE(GLOB sip_files_analysis analysis/*.sip)
 SET(SIP_EXTRA_FILES_DEPEND ${sip_files_core} ${sip_files_analysis})
-SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -o -a ${CMAKE_BINARY_DIR}/python/qgis.analysis.api)
+SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -a ${CMAKE_BINARY_DIR}/python/qgis.analysis.api)
 ADD_SIP_PYTHON_MODULE(qgis.analysis analysis/analysis.sip qgis_core qgis_analysis)
 
 # network-analysis module
 FILE(GLOB sip_files_network_analysis analysis/network/*.sip)
 SET(SIP_EXTRA_FILES_DEPEND ${sip_files_core} ${sip_files_network_analysis})
-SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -o -a ${CMAKE_BINARY_DIR}/python/qgis.networkanalysis.api)
+SET(SIP_EXTRA_OPTIONS ${PYQT4_SIP_FLAGS} -a ${CMAKE_BINARY_DIR}/python/qgis.networkanalysis.api)
 ADD_SIP_PYTHON_MODULE(qgis.networkanalysis analysis/network/networkanalysis.sip qgis_core qgis_networkanalysis)
 
 SET (QGIS_PYTHON_DIR ${PYTHON_SITE_PACKAGES_DIR}/qgis)