Compiling errors

vclock_gettime.c: In function ‘__vdso_time’:
vclock_gettime.c:319:1: error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible
  319 | {
      | ^

Solutions

Switching to gcc-8 should fix the problem:

make CC=gcc-8

References

[1] https://badsimplicity.com/2019/07/10/gcc-9-and-ubuntu-kernel-error/