message: build: remove custom xcode flags for boringssl
  One of the BoringSSL updates we've picked up in the last few months fixed the need for extra flags when compiling BoringSSL in Xcode 9.
  Risk Level: Low
  Testing: existing CI is sufficient
  Release Notes: N/A
diff: set -e
  -# TODO(zuercher): Xcode 9 seems to need this or else boringssl doesn't compile
  -if [[ `uname` == "Darwin" ]];
  -then
  - export CPPFLAGS="$CPPFLAGS -D_DARWIN_C_SOURCE"
  -fi
  -
  COMMIT=664e99a6486c293728097c661332f92bf2d847c6 # chromium-63.0.3239.84
  git clone https://boringssl.googlesource.com/boringssl
  