Move adb to C++.

I keep trying to clean things up and needing std::strings. Might as
well just do this now.

usb_linux_client.c is going to stay as C because GCC isn't smart
enough to deal with the designated initializers it uses (though for
some reason it is in C mode).

The Darwin files are staying as C because I don't have a way to test
that they build.

The Windows files are staying as C because while I can actually build
for them, it's slow and painful.

Change-Id: I75367d29205a9049d34460032b3bb36384f43941
diff --git a/adb/adb_client.h b/adb/adb_client.h
index 6ba3b38..9af176f 100644
--- a/adb/adb_client.h
+++ b/adb/adb_client.h
@@ -47,7 +47,7 @@
  * is zero, or more than one emulator connected (or if you use -s <serial>
  * with a <serial> that does not designate an emulator)
  */
-int  adb_send_emulator_command(int  argc, char**  argv);
+int  adb_send_emulator_command(int  argc, const char**  argv);
 
 /* return verbose error string from last operation */
 const char *adb_error(void);