gdb: fix simulator build failures

gdb: fix simulator build failures

Following reports from me of build failures of the GDB simulator for the
Blackfin architecture, Waldemar cooked a
patch (0005-fix-sim-compile.patch) that removes the typedef of SIM_CPU,
because there was a redefinition of this typedef for Blackfin. This was
not causing an issue with recent compilers as redefining the same
typedef is valid with recent compilers, but was causing build failures
with gcc 4.4.x.

However, by removing the common definition of SIM_CPU, this patch broke
the build of the GDB simulator on other architectures, which did not had
an architecture-specific redefinition of SIM_CPU (unlike Blackfin).

The crux of the problem is in a commit from Mike Frysinger, that tries
to refactor the SIM_CPU definition into a common one. Except that it
leaves a redefinition of it for Blackfin. Removing this second
definition however doesn't easily work, due to include ordering
issues. The easiest solution is to simply revert the patch from Mike
Frysinger. This allows to fix the build for all architectures and all
compiler versions.

Fixes:

  http://autobuild.buildroot.net/results/3b82c44ee853fab0e0c63881f0705bb659412917/
  http://autobuild.buildroot.net/results/dafbb93ab38a4285ce42436219d552cceb14828b/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>