bliss: add spaces to __DATE__ (#17385)

C++11 requires a space between literal and string macro.

var/spack/repos/builtin/packages/bliss/package.py

@@ -24,6 +24,7 @@ class Bliss(Package):
     patch("Makefile.spack.patch")
 
     def install(self, spec, prefix):
+        filter_file('__DATE__', ' __DATE__ ', 'bliss.cc')
         # The Makefile isn't portable; use our own instead
         makeargs = ["-f", "Makefile.spack",
                     "PREFIX=%s" % prefix, "GMP_PREFIX=%s" % spec["gmp"].prefix]