libapps.a needs to be added to the list of libraries to link against.

examples/helloxx/Makefile

@@ -109,7 +109,7 @@ $(CXXOBJS): %$(OBJEXT): %.cxx
 	$(call ARCHIVE, $(BIN), $(OBJS))
 	@touch .built
 
-feq ($(CONFIG_BUILD_KERNEL),y)
+ifeq ($(CONFIG_BUILD_KERNEL),y)
 $(BIN_DIR)$(DELIM)$(PROGNAME): $(OBJS) $(MAINOBJ)
 	@echo "LD: $(PROGNAME)"
 	$(Q) $(LD) $(LDELFFLAGS) $(LDLIBPATH) -o $(INSTALL_DIR)$(DELIM)$(PROGNAME) $(ARCHCRT0OBJ) $(MAINOBJ) $(LDLIBS)

import/Make.defs

@@ -189,7 +189,7 @@ else
   LDLIBPATH = -L $(APPDIR) -L $(TOPDIR)$(DELIM)libs
 endif
 
-LDLIBS = -lnuttx
+LDLIBS = -lapps -lnuttx
 
 # Try to get the path to libgcc.a.  Of course, this only works for GCC
 # toolchains.