* Fix issue with compiling vcpkg.exe (#4149)
The check for environment variable PATH match
other environment variables. When environment variable
VCTargetsPath used by msbuild is changed in cleanEnvironmentHelper.ps1
the path is broken. This makes the compilation of vcpkg.exe fail.
This commit fix the issue by checking that environment variable PATH is
exactly PATH.
* [cleanEnvironmentHelper] Use -eq instead of -match
