pdfium clang/win: Stop passing /FIIntrin.h
pdfium clang/win: Stop passing /FIIntrin.h

See https://codereview.chromium.org/2076483002 for a lengthy reasoning.
The two mysterious files called out there were in boringssl and nacl,
so for pdfium this should be a complete no-op.

BUG=chromium:592745

Review-Url: https://codereview.chromium.org/2096143002

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