BaseTools/CommonLib: Add a step to convert ":\\" to ":\"
BaseTools/CommonLib: Add a step to convert ":\\" to ":\"

Convert ":\\\\" to ":\\", because it doesn't work with WINDOWS_EXTENSION_PATH.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hess Chen <hesheng.chen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com> 


git-svn-id: 3158a46dfd52e07d1fda3e32e1ab2e353a00b20f@16039 6f19259b-4bc3-4df7-8a09-765794883524

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