.travis.yml: add a mingw target

I've include the "big three" softmmu targets x86,arm and ppc.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
.travis.yml: move "make check" to after_script (EXPERIMENTAL)

This moves the problematic make check step to post-build. This means it
can't cause the build to fail. I've also enabled tcg-debug on all builds
for the extra error checking.
target-arm/kvm.c: implement software breakpoints

These don't involve messing around with debug registers, just setting
the breakpoint instruction in memory. GDB will not use this mechanism if
it can't access the memory to write the breakpoint.

--

TODO:
  - still need to add kvm_guest_set_debug to trap bkpts
kmv-all.c: remove pointless malloc check in breakpoint fn

A failure to g_malloc would abort anyway.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>