(maint) Wrap windows PE installation in `cmd /C`

When cygwin converts the posix-style commandline that bash provides to
a windows-style one for calling msiexec, it adds quotes around some
arguments. These quotes cause msiexec to fail. By wrapping the msiexec
invocation in `cmd /C`, we use the windows command interpreter to
handle the command line instead of bash/cygwin. This avoids the
translation issues introduced by cygwin.