Explicitly start gdb with mi2

We should explicitly set the version of mi to use. Until recently
mi == mi2, but with the recent introduction of mi3 as the default
we need to be explicit.

The other place that specifies interpreter is explicit about version
and includes an important comment on the subject

https://github.com/eclipse-cdt/cdt/blob/1590791e76a58ead4d2d7481a5e9a0ff5f83dfab/dsf-gdb/org.eclipse.cdt.dsf.gdb/src/org/eclipse/cdt/dsf/gdb/service/GDBBackend.java#L189-L191

Part of #816

dsf-gdb/org.eclipse.cdt.dsf.gdb/src/org/eclipse/cdt/dsf/gdb/service/GDBBackend_7_12.java

@@ -167,7 +167,7 @@ public String[] getDebuggerCommandLineArray() {
 				"--interpreter", "console", //$NON-NLS-1$ //$NON-NLS-2$
 
 				// Now trigger the new console towards our PTY.
-				"-ex", "new-ui mi " + fMIPty.getSlaveName(), //$NON-NLS-1$ //$NON-NLS-2$
+				"-ex", "new-ui mi2 " + fMIPty.getSlaveName(), //$NON-NLS-1$ //$NON-NLS-2$
 
 				// With GDB.7.12, pagination can lock up the whole debug session
 				// when using the full GDB console, so we turn it off.