Clang msan support #918
Description
Clang ASAN/TSAN support was introduced under #443 and #904.
MSAN isn't going to be easy, and questionably worth doing in our current CI environment. You basically need to rebuild lib[std]c++ and all external deps, see https://github.com/google/sanitizers/wiki/MemorySanitizerLibcxxHowTo. I tried it without this and I see false positives such as:
Uninitialized bytes in __interceptor_strlen at offset 18 inside [0x703000000168, 19)
==7==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x7fe5d4e5d5ce (/google/src/files/151379707/depot/google3/third_party/crosstool/v18/llvm_unstable/toolchain/x86_64-grtev4-linux-gnu/lib64/libstdc++.so.6+0xc75ce)
#1 0x44f11cb (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x44f11cb)
#2 0x4501720 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x4501720)
#3 0x44e7048 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x44e7048)
#4 0x427c0a (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x427c0a)
#5 0x427e91 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x427e91)
#6 0x452d97d (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x452d97d)
#7 0x7fe5d3db4cfe (/usr/grte/v4/lib64/libc.so.6+0x38cfe)
#8 0x639438 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x639438)
Uninitialized value was created by a heap allocation
#0 0x6a86e9 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x6a86e9)
#1 0x7fe5d4e5d668 (/google/src/files/151379707/depot/google3/third_party/crosstool/v18/llvm_unstable/toolchain/x86_64-grtev4-linux-gnu/lib64/libstdc++.so.6+0xc7668)
#2 0x427c0a (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x427c0a)
#3 0x427e91 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x427e91)
#4 0x452d97d (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x452d97d)
#5 0x7fe5d3db4cfe (/usr/grte/v4/lib64/libc.so.6+0x38cfe)
#6 0x639438 (/usr/local/google/home/htuch/.cache/bazel/_bazel_htuch/89676793239ac96d94294e6c7a44597f/execroot/envoy/bazel-out/local-dbg/bin/test/config_test/example_configs_test+0x639438)
SUMMARY: MemorySanitizer: use-of-uninitialized-value (/google/src/files/151379707/depot/google3/third_party/crosstool/v18/llvm_unstable/toolchain/x86_64-grtev4-linux-gnu/lib64/libstdc++.so.6+0xc75ce)
We should consider adding this when we have better CI resourcing for dynamically rebuilding all libraries (so we don't need to bloat the Docker CI image).