In preparation for upgrading to a newer mimalloc version.

Signed-off-by: Matthias Aßhauer <mha1993@live.de>

Update to newer mimalloc versions like this:

  update_mimalloc ()
  {
      test $# = 1 || {
          echo "Need a mimalloc version" 1>&2;
          return 1
      };
      for oneline in 'mimalloc: adjust for building inside Git' 'Import the source code of mimalloc';
      do
          git revert -n HEAD^{/^"$oneline"} && git checkout HEAD -- Makefile && git commit -sm "Temporarily revert \"$oneline\"" -m 'In preparation for upgrading to a newer mimalloc version.' || return 1;
      done;
      for file in $(git show --format='%n' --name-only --diff-filter=A HEAD^{/^"Import the source code of mimalloc "}) compat/mimalloc/arena-abandon.c compat/mimalloc/free.c compat/mimalloc/libc.c compat/mimalloc/prim/prim.c compat/mimalloc/mimalloc-stats.h;
      do
          file2=${file#compat/mimalloc/};
          case "$file2" in
              segment-cache.c)
                  : no longer needed;
                  continue
              ;;
              bitmap.h | *.c)
                  file2=src/$file2
              ;;
              *.h)
                  file2=include/$file2
              ;;
          esac;
          mkdir -p "${file%/*}" && git -C /usr/src/mimalloc/ show "$1":$file2 > "$file" && git add "$file" || {
              echo "Failed: $file2 -> $file" 1>&2;
              return 1
          };
      done;
      conv_sed='sed -n "/^ *eval/d;/      /p"' && git commit -sm "Import the source code of mimalloc $1" -m "Update to newer mimalloc versions like this:" -m "$(set | sed -n '/^update_mimalloc *() *$/,/^}/{s/^./  &/;p}')" -m '  update_mimalloc $MIMALLOC_VERSION' -m 'For convenience, you can set `MIMALLOC_VERSION` and then run:' -m '  eval "$(git show -s <this-commit> | '"$conv_sed"')"' || return 1;
      git cherry-pick HEAD^{/^'mimalloc: adjust for building inside Git'} || return 1
  }

  update_mimalloc $MIMALLOC_VERSION

For convenience, you can set `MIMALLOC_VERSION` and then run:

  eval "$(git show -s <this-commit> | sed -n "/^ *eval/d;/      /p")"

Signed-off-by: Matthias Aßhauer <mha1993@live.de>

We want to compile mimalloc's source code as part of Git, rather than
requiring the code to be built as an external library: mimalloc uses a
CMake-based build, which is not necessarily easy to integrate into the
flavors of Git for Windows (which will be the main benefitting port).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Matthias Aßhauer <mha1993@live.de>

Stable Mimalloc releases will start with 3.2.x, so we don't need to
monitor 3.0 and 3.1.

Signed-off-by: Matthias Aßhauer <mha1993@live.de>