* Debug: Actually use the --32 and --64 command line arguments

* debug: make XLEN mismatch message clearer

misa is allowed to be hardwired to 0, so checking its U bit could
incorrectly suggest that U-mode is not supported.

When not passed, they are no longer printed out.

* debug: Need to apply remotetimeout before connecting to remote target

* debug: whitespace cleanup

Closes #89

This test would fail intermittently if gdb on the first hart managed to
set a breakpoint, resume, halt, and clear the breakpoint before the
second hart got a chance to resume.

Temporarily comment out MulticoreRegTest due to flakiness.

Follow-up to b68b3903.

The 64KiB allocated by the code to force a cache miss makes it impossible to run
the test from any memories that are smaller 64KiB, such as scratchpad memories
or LIMs. Since this is trying to test microarchitectural behavior, they don't
belong in these ISA tests anyway.

This allows them to be referenced by other files, such as a test environment
that lives in a separate compilation unit.

I need this for CompareSections to pass when I instrument spike to be
really slow.

Fixes #83.

Multigdb support

Now on multi-core targets it only runs once, wasting less time.

The Gdb class now can handle connecting to more than one gdb. It
enumerates the harts across all connections, and when asked to select a
hart, it transparently sends future gdb commands to the correct
instance.

Multicore tests still have to be aware of some differences. The main one
is that when executing 'c' in RTOS mode, all harts resume, while in
multi-gdb mode only the current one resumes. Additionally, gdb doesn't
set breakpoints until 'c' is issued, so the hart where breakpoints are
set needs to be resumed before other harts might see them.

Some boards have jumpers that control the reset vector, and forcing them
one way or another is more annoying than dealing with it in software.

Add interrupts to MulticoreRunHaltStepiTest.

Fixes #77.

Just to hammer on anything at once, and hopefully catch weird
interactions if they exist.