Removed "undefined" argument for Apple platforms.

This is incompatible with enabling bitcode, such as with iOS builds. The
default value for "undefined" is "error" so this option should be
redundant.

CMakeLists.txt

@@ -695,7 +695,6 @@ if(USE_GCC OR USE_CLANG)
     cmake_pop_check_state()
 
     # FIXME: use generator expression instead of appending to EXTRA_LDFLAGS_BUILD
-    list(APPEND EXTRA_LDFLAGS_BUILD "-Wl,-undefined,error")
     list(APPEND EXTRA_LDFLAGS_BUILD "-Wl,-compatibility_version,${DYLIB_COMPATIBILITY_VERSION}")
     list(APPEND EXTRA_LDFLAGS_BUILD "-Wl,-current_version,${DYLIB_CURRENT_VERSION}")
   elseif(NOT OPENBSD)