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GH-37410: [C++][Gandiva] Add support for using LLVM shared library (#37412)

### Rationale for this change

Gandiva always links LLVM statically. But we can use LLVM shared library instead to reduce `libgandiva.so` size.

### What changes are included in this PR?

Add `ARROW_LLVM_USE_SHARED` like other dependencies.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes.

This has a backward incompatible change. LLVM shared library not static libraries is used by default. If you want to use LLVM static libraries, you need to specify `-DARROW_LLVM_USE_SHARED=OFF` or `-DARROW_DEPENDENCY_USE_SHARED=OFF` explicitly.
* Closes: #37410

Lead-authored-by: Sutou Kouhei <kou@clear-code.com>
Co-authored-by: Sutou Kouhei <kou@cozmixng.org>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>