win,nfc: use #pragma warnings() for MSVC only
win,nfc: use #pragma warnings() for MSVC only

PR-URL: https://github.com/libuv/libuv/pull/2854
Reviewed-By: Anna Henningsen <2bc1ecb410e142bce83bce6f212b41e1781536dc@addaleax.net>
Reviewed-By: Bartosz Sosnowski <aa4e0bd35c562885f21ad74b171c23cfc4370e31@janeasystems.com>
Reviewed-By: Jameson Nash <99e7f19e9f64df56d4e81dc00b8566e722cdd766@gmail.com>
Co-authored-by: Anna Henningsen <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@addaleax.net>

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