Use correct 64bit full multiplication for MinGW on ARM64

[vejbomar]

Update fast_float code from charconv to use correct 64bit full multiplication for MinGW on ARM64.

PR that did the same in charconv: boostorg/charconv#230

[cppalliance-bot]

An automated preview of the documentation is available at https://1057.jsondocs.prtest.cppalliance.org/libs/json/doc/html/index.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.41%. Comparing base (5bdbb23) to head (b6c916f).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1057   +/-   ##
========================================
  Coverage    93.41%   93.41%           
========================================
  Files           91       91           
  Lines         8667     8667           
========================================
  Hits          8096     8096           
  Misses         571      571           

Files with missing lines	Coverage Δ
...detail/charconv/detail/fast_float/float_common.hpp	62.19% <ø> (ø)

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1057/pullrequest.html

[grisumbras]

Thank you for your contribution.