[COFF] Initalize ErrorHandler with CanExitEarly value

Previously, the COFF driver would call exit(1) from the
ErrorHandler in the case of a link error, even if
CanExitEarly=false was specified. Now it initializes
the ErrorHandler in the same way that the ELF driver does.

Patch by Andrew Kelley.

Differential Revision: https://reviews.llvm.org/D41803

llvm-svn: 321983