BUG: fix weave issue with too long file names with MSVC.  Closes gh-3216.

This issue was introduced in 021e0ee15.  It's MSVC specific; MSVC
has a 260 char file name (including full path).  So truncation the
has to 50 chars, plus filename prefix (``sc_`` or ``compiler_``), leaves
200 chars for the path which should be enough.