Fix gnulib intprops problem
Taken from gnulib commit
commit b9c364f02cb7a7485cd063fa2cbcbf82042fa8cc
Author: Jim Meyering <meyering@fb.com>
Date: Mon Aug 29 09:27:50 2016 -0700
intprops.h: fix missing-backslash problems
* lib/intprops.h (_GL_ADD_OVERFLOW): Add backslash.
(_GL_SUBTRACT_OVERFLOW,_GL_MULTIPLY_OVERFLOW): Likewise.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>