Detect a Cxc build from the options and automatically disabled installing.

This is similar to always providing --no-install on the command when building
a Cxc package.

source-builder/sb/options.py

@@ -297,6 +297,10 @@ class command_line:
             rsb_macros = path.join(os.environ['HOME'], '.rsb_macros')
             if path.exists(rsb_macros):
                 self.defaults.load(rsb_macros)
+        # If a Cxc build disable installing.
+        if self.canadian_cross():
+            self.opts['no-install'] = '1'
+            self.defaults['_no_install'] = '1'
 
     def sb_git(self):
         repo = git.repo(self.defaults.expand('%{_sbdir}'), self)
@@ -360,6 +364,15 @@ class command_line:
     def no_install(self):
         return self.opts['no-install'] != '0'
 
+    def canadian_cross(self):
+        _host = self.defaults.expand('%{_host}')
+        _build = self.defaults.expand('%{_build}')
+        _target = self.defaults.expand('%{_target}')
+        if len(_target):
+            return len(_host) and len(_build) and (_target) and \
+                _host != _build and _host != _target
+        return len(_host) and len(_build) and _host != _build
+
     def user_macros(self):
         #
         # Return something even if it does not exist.

source-builder/sb/setbuilder.py

@@ -458,8 +458,10 @@ def run():
             deps = None
         if not list_bset_cfg_files(opts, configs):
             prefix = opts.defaults.expand('%{_prefix}')
-            if not opts.dry_run() and not opts.no_install() and \
+            if not opts.dry_run() and \
-                    not path.ispathwritable(prefix):
+               not not opts.canadian_cross() and \
+               not opts.no_install() and \
+               not path.ispathwritable(prefix):
                 raise error.general('prefix is not writable: %s' % (path.host(prefix)))
             for bset in opts.params():
                 setbuilder_error = True