Switch over to the google3 unix_file File*.

I also moved macros.h to base/macros.h to ease google3 porting, at
the expense of a larger than necessary change. (I learned my lesson,
though, and didn't make the equivalent base/logging.h change.)

I'm not sure whether we want to keep the unix_file MappedFile given
our existing MemMap, but it's easier to bring it over and then remove
it (and possibly revert the removal) than to bring it over later.

Change-Id: Id50a66faa5ab17b9bc936cc9043dbc26f791f0ca
diff --git a/src/logging.h b/src/logging.h
index 1c04b2c..55dc710 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -22,8 +22,8 @@
 #include <iostream>  // NOLINT
 #include <sstream>
 #include <signal.h>
+#include "base/macros.h"
 #include "log_severity.h"
-#include "macros.h"
 
 #define CHECK(x) \
   if (UNLIKELY(!(x))) \