[scudo] Fix standlone build -lrt requirement

[cryptoad]

Summary

The split in D39461 introduced separate C++ flags, but cxx_flags needs -lrt as well for the standalone build.

[cryptoad]

Same idea, but with just line reordering.

test/scudo/lit.cfg

c_flags = ([config.target_cflags] +
            "-UNDEBUG",
            "-ldl",
            "-Wl,--gc-sections"])
 cxx_flags = (c_flags + config.cxx_mode_flags + ["-std=c++11"])
 
 # Android doesn't want -lrt.
 if not config.android:
   c_flags += ["-lrt"]
+  cxx_flags += ["-lrt"]
 
 def build_invocation(compile_flags):                                            
   return " " + " ".join([config.compile_wrapper, config.clang] + compile_flags) + " "                   
 
 # Add clang substitutions.
 config.substitutions.append(("%clang ", build_invocation(c_flags)))
 config.substitutions.append(("%clang_scudo ", build_invocation(c_flags) + whole_archive))
 config.substitutions.append(("%clangxx_scudo ", build_invocation(cxx_flags) + whole_archive + whole_archive_cxx))