Windows: Link with /MT or /MTd

[Johan Engelen via digitalmars-d-ldc]

Note that druntime 2.067 explicitly links with the release 
version libcmt.lib  (druntime/src/rt/monitor_.d(58): "pragma(lib, 
"libcmt.lib");").

LDC-merge2.067 does not link executables on Windows because of a 
library conflict due to that pragma. LDC does not need that 
pragma, and commenting out that pragma avoids the conflict.