When `llvm-symbolizer.exe` is on the PATH in an entry containing two
consecutive backslashes, sanitizers will try to launch llvm-symbolizer
with its absolute path containing these consecutive backslashes. This
fails a sanity check in `sanitizer_symbolizer_win.cpp`.
According to the documentation of `CommandLineToArgvW`  and a MS blog
post , backslashes in general, regardless of how many of them in a
row, do not have any special effect, unless when immediately followed by
a double quote.
There already exists a check that fails when the command line arguments
contains double quote, therefore the check for double backslashes can
simply be removed.