Make bundling Microsoft_VC100_CRT_x86.msm truly optional

[Stephan Bergmann]

<http://cgit.freedesktop.org/libreoffice/core/commit/?id=6cfe3c93dc55264e57f1057a2911d54232353d13> 
"Make bundling Microsoft_VC100_CRT_x86.msm truly optional" should 
prevent builds from failing on machines where no 
Microsoft_VC100_CRT_x86.msm is available.

However, I could not check whether it does not cause any regressions on 
machines that /do/ have Microsoft_VC100_CRT_x86.msm (i.e., would stop 
bundling it there and break 
<https://bugs.freedesktop.org/show_bug.cgi?id=50584> "LibreOffice says 
that Java runtime JRE 1.7 on Windows is defective" again).  If anybody 
with such a machine could please have a look...

Thanks,
Stephan