Generate shorter string literals

This is related to <http://trac.cython.org/cython_trac/ticket/50>.

Cython 0.12.1 still generates string literals that can be too long for MSVC*
compilers. Please consider the following patch.

Cython/Compiler/Code.py

@@ -667,7 +667,7 @@ class GlobalState(object):
         decls_writer = self.parts['decls']
         for _, cname, c in c_consts:
             decls_writer.putln('static char %s[] = "%s";' % (
-                cname, c.escaped_value))
+                cname, StringEncoding.split_docstring(c.escaped_value)))
             if c.py_strings is not None:
                 for py_string in c.py_strings.itervalues():
                     py_strings.append((c.cname, len(py_string.cname), py_string))