Added a new c++-template-depth Boost Build feature allowing configuring compilers supporting this feature with the maximal template instantiation depth. Currently supported for gcc & qcc toolsets.

[SVN r47727]

tools/build

@@ -1 +1 @@
-Subproject commit fd0ff0e6681a24b9e73abf0a827aad8073d09000
+Subproject commit 4c121da45fd10fcfdb9c56235842778f51a66d4c