post-merge build is broken

[derekargueta]

Seems it doesn't like something about tcmalloc

Use --sandbox_debug to see verbose messages from the sandbox
warning: unknown warning option '-Wno-implicit-int-float-conversion'; did you mean '-Wno-implicit-float-conversion'? [-Wunknown-warning-option]
In file included from external/com_github_google_tcmalloc/tcmalloc/cpu_cache.cc:15:
In file included from external/com_github_google_tcmalloc/tcmalloc/cpu_cache.h:30:
external/com_github_google_tcmalloc/tcmalloc/internal/percpu_tcmalloc.h:332:18: error: invalid output constraint '=@ccae' in asm
      [overflow] "=@ccae"(overflow)
                 ^
external/com_github_google_tcmalloc/tcmalloc/internal/percpu_tcmalloc.h:459:25: error: invalid output constraint '=@ccbe' in asm
            [underflow] "=@ccbe"(underflow),
                        ^
1 warning and 2 errors generated.
Target //:envoy failed to build
INFO: Elapsed time: 52.329s, Critical Path: 21.65s
INFO: 2526 processes: 2130 internal, 395 processwrapper-sandbox, 1 worker.
FAILED: Build did NOT complete successfully
FAILED: Build did NOT complete successfully

did a bit of bisecting and I think it started with this commit in main Envoy: https://github.com/envoyproxy/envoy/commit/4c0d2d2a36996f2ec7d00b519ea90068629a2c55'

envoy-filter-example commit: https://github.com/envoyproxy/envoy-filter-example/commit/db2cdca49e2546eca58006c3a01f1b3e8777f39d

[robinp-tw]

Using clang-10 seems to help me:

bazel clean --expunge
CC=clang-10 bazel build -c opt //source/exe:envoy