[Pkg-uml-pkgs] Bug#887761: user-mode-linux FTBFS with glibc 2.26

[Adrian Bunk]

Source: user-mode-linux
Version: 4.14-1um-1
Severity: serious

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/user-mode-linux.html

...
  CC      arch/um/os-Linux/signal.o
arch/um/os-Linux/signal.c: In function 'hard_handler':
arch/um/os-Linux/signal.c:163:22: error: dereferencing pointer to incomplete type 'struct ucontext'
  mcontext_t *mc = &uc->uc_mcontext;
                      ^~
scripts/Makefile.build:319: recipe for target 'arch/um/os-Linux/signal.o' failed
make[2]: *** [arch/um/os-Linux/signal.o] Error 1