Bazel client: depend less on <unistd.h>

We moved most of the functionality (e.g. _exit,
SetupStreams) into blaze_util_<platform> or
changed to alternative functions (fwrite + stderr
instead of write + STDERR_HANDLE).

This change brings us closer to compiling blaze.cc
with MSVC. We still have to move signal handlers
out of blaze.cc as well as code dealing with the
server PID.

See https://github.com/bazelbuild/bazel/issues/2107

--
MOS_MIGRATED_REVID=140123945
diff --git a/src/main/cpp/blaze_util.h b/src/main/cpp/blaze_util.h
index e294a42..06c75ed 100644
--- a/src/main/cpp/blaze_util.h
+++ b/src/main/cpp/blaze_util.h
@@ -118,7 +118,7 @@
 // Returns true iff arg is a valid command line argument for bazel.
 bool IsArg(const std::string& arg);
 
-// Converts a project identifier to string.
+// Returns the string representation of `value`.
 // Workaround for mingw where std::to_string is not implemented.
 // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52015.
 template <typename T>