Chromium uses GN's default configs feature which makes all targets default to a
set of configs. It then expects third_party code to take one of them
(chromium_code) out and put in a different one (no_chromium_code).
Because of that, we need a way to tell the template to emit -= lines. Add a
separate option for that.
(It may be worth making us clean against the chromium_code config rather than
the no_chromium_code one, but I'll explore that separately in case making the C
code clean ends up being a rabbithole.)
BUG=chromium:607294
Change-Id: I2aa179665ab17439cc123fc86a7af9690cd4bcd6
Reviewed-on: https://boringssl-review.googlesource.com/7795
Reviewed-by: Adam Langley <agl@google.com>
b3be1cf97d