Configurable client meta-data (#662)

This provide a way to configure snmalloc to provide per object meta-data that is out of band. This can be used to provide different mitigations on top of snmalloc, such as storing memory tags in a compressed form, or provide a miracle pointer like feature.

This also includes a couple of TSAN fixes as it wasn't fully on in CI.

.github/workflows/main.yml

@@ -224,15 +224,14 @@ jobs:
       matrix:
         # Build just release variant as Debug is too slow.
         build-type: [ Release ]
+        os: ["ubuntu-latest", "ubuntu-20.04"]
         include:
           - os: "ubuntu-latest"
-            continue-on-error: # Don't class as an error if this fails, until we have a more reliablity.
             variant: "libc++ (TSan + UBSan)"
             dependencies: "sudo apt install ninja-build"
             extra-cmake-flags: "-DCMAKE_CXX_COMPILER=clang++ -DCMAKE_CXX_FLAGS=-stdlib=\"libc++ -g\" -DSNMALLOC_SANITIZER=undefined,thread"
           # Also test specifically with clang-10 (on ubuntu-20.04)
           - os: "ubuntu-20.04"
-            continue-on-error: # Don't class as an error if this fails, until we have a more reliablity.
             variant: "clang-10 libc++ (TSan + UBSan)"
             dependencies: "sudo apt install ninja-build"
             extra-cmake-flags: "-DCMAKE_CXX_COMPILER=clang++-10 -DCMAKE_CXX_FLAGS=-stdlib=\"libc++ -g\" -DSNMALLOC_SANITIZER=undefined,thread"
@@ -452,7 +451,7 @@ jobs:
         git diff --exit-code
     - name: Run clang-tidy
       run: |
-        clang-tidy-15  src/snmalloc/override/malloc.cc  -header-filter="`pwd`/*" -warnings-as-errors='*' -export-fixes=tidy.fail -- -std=c++17 -mcx16 -DSNMALLOC_PLATFORM_HAS_GETENTROPY=0
+        clang-tidy-15  src/snmalloc/override/malloc.cc  -header-filter="`pwd`/*" -warnings-as-errors='*' -export-fixes=tidy.fail -- -std=c++17 -mcx16 -DSNMALLOC_PLATFORM_HAS_GETENTROPY=0 -Isrc
         if [ -f tidy.fail ] ; then
           cat tidy.fail
           exit 1