gen_msvs_vcxproj.sh: add --enable-werror option

translates to TreatWarningAsError (/WX)
setting this via the CL environment variable is not possible due to the
/WX- default which is used on the command line

Change-Id: I0b42a9d3ca9eba6af82c25b8e434baa2fcb00156
2 files changed