The facedetect plugin cannot be built with C++11:

frei0r-plugins-1.5.0/src/filter/facedetect/facedetect.cpp:271:15: 
  error: non-constant-expression cannot be narrowed from type 'int' 
  to 'double' in initializer list [-Wc++11-narrowing]

--- src/filter/facedetect/CMakeLists.txt.orig	2018-01-17 09:42:26 UTC
+++ src/filter/facedetect/CMakeLists.txt
@@ -11,5 +11,6 @@ LINK_LIBRARIES(${OpenCV_LIBS} ${OpenCV_LIBRARIES})
 
 add_library (${TARGET}  MODULE ${SOURCES})
 set_target_properties (${TARGET} PROPERTIES PREFIX "")
+set_property(TARGET facedetect PROPERTY CXX_STANDARD 98)
 
 install (TARGETS ${TARGET} LIBRARY DESTINATION ${LIBDIR})
