Comment 3 for bug 1848594

Still not fixed in 6.0.14-dfsg-2.

In file included from <<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.c:31:
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.c: In function 'VBoxGuest_RTMemContAlloc':
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/the-linux-kernel.h:340:47: error: implicit declaration of function 'set_pages_x'; did you mean 'set_pages_rw'? [-Werror=implicit-function-declaration]
  340 | # define MY_SET_PAGES_EXEC(pPages, cPages) set_pages_x(pPages, cPages)
      | ^~~~~~~~~~~
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.c:447:13: note: in expansion of macro 'MY_SET_PAGES_EXEC'
  447 | MY_SET_PAGES_EXEC(&paPages[iPage], 1);
      | ^~~~~~~~~~~~~~~~~
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.c: In function 'VBoxGuest_RTMemContFree':
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/the-linux-kernel.h:341:47: error: implicit declaration of function 'set_pages_nx'; did you mean 'set_pages_rw'? [-Werror=implicit-function-declaration]
  341 | # define MY_SET_PAGES_NOEXEC(pPages, cPages) set_pages_nx(pPages, cPages)
      | ^~~~~~~~~~~~
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.c:495:13: note: in expansion of macro 'MY_SET_PAGES_NOEXEC'
  495 | MY_SET_PAGES_NOEXEC(&paPages[iPage], 1);
      | ^~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[3]: *** [scripts/Makefile.build:273: <<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/alloc-r0drv-linux.o] Error 1
make[3]: *** Waiting for unfinished jobs....
<<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest/r0drv/linux/memuserkernel-r0drv-linux.o: warning: objtool: rtR0MemKernelCopyLnxWorker()+0x15: redundant CLD
make[2]: *** [scripts/Makefile.build:531: <<DKMSDIR>>/build/virtualbox-guest/6.0.14/build/vboxguest] Error 2
make[1]: *** [Makefile:1681: <<DKMSDIR>>/build/virtualbox-guest/6.0.14/build] Error 2
make[1]: Leaving directory '<<DKMSDIR>>/headers/linux-headers-5.4.0-7-generic'

Looks like it's been fixed upstream:

https://www.virtualbox.org/ticket/18945