Define WIN32_LEAN_AND_MEAN in the build system, not in the code.

This avoids a conflict with the Chromium build system, which
defines WIN32_LEAN_AND_MEAN with a different value.

BUG=crbug.com/453196

Change-Id: Ia15ec7c20325c1961af4f32e5208266e5f846f35
Reviewed-on: https://boringssl-review.googlesource.com/3150
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
14 files changed