tests: Add an implementation of the Logger interface for use gtests.

On exiting log types (panic and fatal), the message is set to an
ADD_FAILURE_AT macro, and the test is exited by throwing an otherwise
unexpected exception. On non-exiting log types, the message is sent to
the SUCCEEDED macro which currently doesn't output anything.

Change-Id: I1bb569e6cb8308dbc4c3e04eea7a962bd2b1ddd8
Reviewed-on: https://gem5-review.googlesource.com/6264
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

src/base/SConscript

@@ -40,7 +40,7 @@ Source('bigint.cc')
 Source('imgwriter.cc')
 Source('bmpwriter.cc')
 Source('callback.cc')
-Source('cprintf.cc')
+Source('cprintf.cc', add_tags='gtest lib')
 Source('debug.cc')
 if env['USE_FENV']:
     Source('fenv.c')