ci/style-check: add `RemoveBracesLLVM` in CI job

ci/style-check: add `RemoveBracesLLVM` in CI job

For 'clang-format', setting 'RemoveBracesLLVM' to 'true', adds a check
to ensure we avoid curly braces for single-statement bodies in
conditional blocks.

However, the option does come with two warnings [1]:

    This option will be renamed and expanded to support other styles.

and

    Setting this option to true could lead to incorrect code formatting
    due to clang-format’s lack of complete semantic information. As
    such, extra care should be taken to review code changes made by
    this option.

The latter seems to be of concern. While we want to experiment with the
rule, adding it to the in-tree '.clang-format' could affect end-users.
Let's only add it to the CI jobs for now. With time, we can evaluate
its efficacy and decide if we want to add it to '.clang-format' or
retract it entirely. We do so, by adding the existing rules in
'.clang-format' and this rule to a temp file outside the working tree,
which is then used by 'git clang-format'. This ensures we don't murk
with files in-tree.

[1]: https://clang.llvm.org/docs/ClangFormatStyleOptions.html#removebracesllvm

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>