Make the variant and toolset tag logic common. Add generic tag formating rule that can be used from specific tag rules to generate a variety of target names.

[SVN r35529]

tools/build

@@ -1 +1 @@
-Subproject commit e7657608f4df466dcba568fe643e475b38de8478
+Subproject commit 6a9aac8a793c06d3ae0c234de730e4b7dc827c64