fix Issue 10746 - Win64: corrupt debug info with very long symbols

Function literals used as alias template arguments print their code into the "pretty" symbol name of the template instance, which can cause very long symbol names. Lacking any other compression this corrupts the CV8 debug info.

This patch cuts the length of the symbols in the output to just below 65500 bytes.

http://d.puremagic.com/issues/show_bug.cgi?id=10746