Win64: no error status when creating a library fails

[rainers]

Here's a repro:

C:\tmp\d\ldc>ldc2 -lib test.d
C:\tmp\d\ldc>attrib +R test.lib
C:\tmp\d\ldc>ldc2 -lib test.d
LINK : fatal error LNK1104: cannot open file 'test.lib'
Error: C:\l\vs14\VC\BIN\lib.exe failed with status: 1104

C:\tmp\d\ldc>echo %ERRORLEVEL%
0

ldc sould return an error here, probably the status of the failing lib call.

[dnadlinger]

Fixed by #1162, thanks!

(By the way, if you include something to the effect of closes #<issue_id> or fixes #<issue_id> in the commit message, the PR will be linked with the issue automatically.)