Add ppc64le runs to CI

[mborland]

Closes: #633

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.2%. Comparing base (03b81f3) to head (11115ac).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop    #700   +/-   ##
=======================================
  Coverage     99.2%   99.2%           
=======================================
  Files          230     230           
  Lines        16290   16290           
  Branches      1757    1757           
=======================================
  Hits         16145   16145           
  Misses         145     145           

Files	Coverage Δ
...clude/boost/decimal/detail/ryu/ryu_generic_128.hpp	97.6% <ø> (ø)
test/test_beta.cpp	100.0% <100.0%> (ø)
test/test_decimal32_fast_stream.cpp	100.0% <ø> (ø)
test/test_decimal32_stream.cpp	100.0% <ø> (ø)
test/test_snprintf.cpp	100.0% <ø> (ø)
test/test_strtod.cpp	100.0% <ø> (ø)

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