Provide a SplitCommandLine method in the option processor
that takes a given command line args and splits it into the corresponding
{binary, startup_args, command, command_args}.

The purpose of this function is to help split the responsibilities
of the ParseOptions function by processing the startup options independently
(i.e. rc files detection and processing) from the command options.
This will be combined with ParseOptions in a subsequent CL.

--
MOS_MIGRATED_REVID=139773786
diff --git a/src/main/cpp/blaze_util.h b/src/main/cpp/blaze_util.h
index eee40f9..666b06e 100644
--- a/src/main/cpp/blaze_util.h
+++ b/src/main/cpp/blaze_util.h
@@ -115,6 +115,9 @@
 bool CheckJavaVersionIsAtLeast(const std::string &jvm_version,
                                const std::string &version_spec);
 
+// Returns true iff arg is a valid command line argument for bazel.
+bool IsArg(const std::string& arg);
+
 // Converts a project identifier to string.
 // Workaround for mingw where std::to_string is not implemented.
 // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52015.