PR 2108, PR 2109. Add --jobs and --always-clean.

Refactor the options handling in defaults.py to allow the --jobs
option have varing specific parameters. The option supports 'none',
'max' and 'half' or a fraction to divide the number of CPUs or
an integer value which is the number of jobs. The --no-smp has
been removed.

The host specific modules have been changed to set the number of
CPUs in the defaults table.

Fixed the --keep-going to clean up is --always-clean is provided
even if the build has an error.

source-builder/sb/windows.py

@@ -58,15 +58,12 @@ def load():
             pass
 
     if os.environ.has_key('NUMBER_OF_PROCESSORS'):
-        ncpus = int(os.environ['NUMBER_OF_PROCESSORS'])
+        ncpus = os.environ['NUMBER_OF_PROCESSORS']
     else:
-        ncpus = 0
-    if ncpus > 1:
-        smp_mflags = '-j' + str(ncpus)
-    else:
-        smp_mflags = ''
+        ncpus = '1'
 
     defines = {
+        '_ncpus':         ('none',    'none',     ncpus),
         '_os':            ('none',    'none',     'win32'),
         '_build':         ('triplet', 'required', build_triple),
         '_host':          ('triplet', 'required', host_triple),