Fix the host-specific installation destdir for build-script products.

Prior to this, build-script products that build in the host-specific
directories for cross-compilation would get the wrong path, and
therefore wouldn't get picked up in toolchain builds.

Author: DougGregor

utils/swift_build_support/swift_build_support/products/product.py

@@ -224,7 +224,7 @@ def host_install_destdir(self, host_target):
                 # If this is one of the hosts we should lipo,
                 # install in to a temporary subdirectory.
                 return '%s/intermediate-install/%s' % \
-                    (self.args.install_destdir, host_target)
+                    (os.path.dirname(self.build_dir), host_target)
             elif host_target == "merged-hosts":
                 # This assumes that all hosts are merged to the lipo.
                 return self.args.install_destdir