envoy: mark as broken

building
Extracting Bazel installation...
Loading:
Analyzing: target //source/exe:envoy-static
ERROR: java.io.IOException: Could not read the crosstool configuration file 'CROSSTOOL file /tmp/nix-build-envoy-1.3.0.drv-0/envoy-v1.3.0-src/.home/.cache/bazel/_bazel_nixbld1/cbe181aaebf3d7253cbcf6057028e514/external/local_config_cc/CROSSTOOL', because of a parser error (945:1: Expected identifier. Found '%')
INFO: Elapsed time: 3.065s
FAILED: Build did NOT complete successfully
builder for ‘/nix/store/09wh9hd81529pgr3ddwfw68higfzkfgr-envoy-1.3.0.drv’ failed with exit code 2
error: build of ‘/nix/store/09wh9hd81529pgr3ddwfw68higfzkfgr-envoy-1.3.0.drv’ failed