build/msvs: fix builds in source dirs with spaces

...when configured below the path containing spaces. configuring outside
the path containing spaces still won't work due to issues with the
makefiles, e.g.,
/path with spaces/git
/path with spaces/build1
/build2
configure/make in build1 will work, build2 will not

Change-Id: Ie4a1f313596d7457cadd67476ac1dbd3273ad46e