Difference between constexpr and static constexpr global variable

In the C++11 standard, what is the difference between constexpr and static constexpr global variables when defined in a header? More specifically, when multiple translation units include the same header, which declaration (if any) is guaranteed to define the same variable across the translation units?

e.g.,

cexpr.h:

#ifndef CEXPR_H
#define CEXPR_H

constexpr int cint = 1;
static constexpr int scint = 1;

#endif

a.cpp:

#include "cexpr.h"

b.cpp:

#include "cexpr.h"