arm64: msac: Add handwritten versions of msac_decode_bool functions

GCC                     Cortex A53   A72   A73
msac_decode_bool_c:           29.9  17.9  23.2
msac_decode_bool_neon:        27.4  15.3  20.4
msac_decode_bool_adapt_c:     49.2  26.8  31.0
msac_decode_bool_adapt_neon:  38.2  22.2  25.4
msac_decode_bool_equi_c:      26.6  16.8  19.4
msac_decode_bool_equi_neon:   23.9  13.7  15.7

Clang                   Cortex A53   A72   A73
msac_decode_bool_c:           28.0  16.4  23.1
msac_decode_bool_neon:        26.9  14.6  21.0
msac_decode_bool_adapt_c:     46.8  25.1  31.4
msac_decode_bool_adapt_neon:  36.2  19.0  26.2
msac_decode_bool_equi_c:      23.7  13.4  18.8
msac_decode_bool_equi_neon:   23.7  11.3  14.2

This is as fast as, or faster than, what either GCC or Clang
produces.
22 jobs for master in 8 minutes and 11 seconds (queued for 31 seconds)
Status Job ID Name Coverage
  Style
passed #278779
debian amd64
style-check

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  Build
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debian amd64
build-debian

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debian aarch64
build-debian-aarch64

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build-debian-aarch64-clang-5

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build-debian-static

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build-debian-werror

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build-debian32

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macos
build-macos

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debian amd64 allowed to fail
build-ubuntu-snap

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debian amd64
build-win-arm32

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debian amd64
build-win-arm64

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build-win32

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debian amd64
build-win32-unaligned-stack

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debian amd64
build-win64

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  Test
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debian amd64
test-debian

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passed #278797
debian amd64
test-debian-asan

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debian amd64
test-debian-msan

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debian amd64
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debian amd64
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debian amd64
test-win64

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