[msan] Add 32-bit platforms support (#109284)
References https://github.com/llvm/llvm-project/issues/103057
Added `VAArgHelper` functions for platforms: ARM32, i386, RISC-V,
PowerPC32, MIPS32.
ARM, RISCV and MIPS share similar conventions regarding va args.
Therefore `VAArgGenericHelper` was introduced to avoid code duplication.
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Co-authored-by: Kamil Kashapov <kashapov@ispras.ru>
Co-authored-by: Vitaly Buka <vitalybuka@google.com>
