Fix MSVC build
Fix MSVC build

Was wrongly assuming that if ..\deqp exists, the build directory must
be deqp\build.

Change-Id: I0e071565d9c41940efbcd4453de70f2994ad1be5
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27652
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader