Add Windows specific waf support for MSYS2.

Limit the compilers used to gcc and clang. Clang has not been tested.
Users with MSVC install does not need to remove now.

Force the os.sep path to the standard '\\' on Windows. The MSYS2 python
sets it to '/' for internal project reasons. Doing this does cause waf
problems when running configure so only do this for the build target.

Closes #2583.

tools/gdb/python/wscript

@@ -2,6 +2,9 @@
 # Install the RTEMS gdb python
 #
 
+def init(ctx):
+    pass
+
 def options(opt):
     opt.load('python')