mckernel overlay: replace mcoverlayfs with a soft userspace overlay

mcoverlayfs has a high maintenance burden and does not work on rhel8's 4.18
kernel (while it works on vanilla 4.18...); instead of debugging this further
time is better spent making it independent from overlayfs.

Change-Id: I7454ae95b0fbb3373c256aa2fd83cdfec466c009

executer/user/arch/arm64/Makefile.in

@@ -10,15 +10,12 @@ LIBS=@LIBS@
 
 all: $(TARGET)
 
-../../libmcexec.a: archdep.o arch_syscall.o
-	$(AR) cr ../../libmcexec.a archdep.o arch_syscall.o
+../../libmcexec.a: archdep.o
+	$(AR) cr ../../libmcexec.a archdep.o
 
 archdep.o: archdep.c archdep.S
 	$(CC) -c -I${KDIR} $(CFLAGS) $(EXTRA_CFLAGS) -fPIE -pie -pthread $^
 
-arch_syscall.o: arch_syscall.c
-	$(CC) -c -I${KDIR} $(CFLAGS) $(EXTRA_CFLAGS) -fPIE -pie -pthread $<
-
 clean:
 	$(RM) $(TARGET) *.o
 

executer/user/arch/arm64/arch_syscall.c

@@ -1,7 +0,0 @@
-struct syscall_wait_desc;
-
-int
-archdep_syscall(struct syscall_wait_desc *w, long *ret)
-{
-	return -1;
-}