XXX push upstream
There's another check for BSD later on in the file; it should use it.

Index: cmake/modules/SetupBuildFlags.cmake
--- cmake/modules/SetupBuildFlags.cmake.orig
+++ cmake/modules/SetupBuildFlags.cmake
@@ -20,7 +20,6 @@ macro(setup_build_flags _maintainer_mode)
 		-Wundef
 		-Wwrite-strings
 		-Wno-cast-function-type
-		-Wl,--no-undefined
 		-fno-strict-aliasing
 	)