GN: Add __STDC_LIMIT_MACROS to nacl_defines for Windows
GN: Add __STDC_LIMIT_MACROS to nacl_defines for Windows

Some of the NaCl trusted code uses <stdint.h> macros, and
these are not available by default on Windows.

BUG= 512869
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/1426663003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356648}

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