Made BOOST_CHARCONV_HAS_QUADMATH a usage requirement in the Jamfile

[anarthal]

Removed unnecessary BOOST_CHARCONV_NO_QUADMATH macro definition from CMake
Changed all BOOST_CHARCONV_HAS_FLOAT128 usages into BOOST_CHARCONV_HAS_QUADMATH, which is guaranteed to be correctly propagated
Fixed tests that had missing includes, unnoticed due to being ifdef-ed out by BOOST_CHARCONV_HAS_QUADMATH

close #249

[anarthal]

• Note that the BOOST_CHARCONV_NO_QUADMATH CMake option is still valid and working. I've only removed the C++ macro definition it caused, as it's not used and doesn't have an equivalent in the Jamfile.
• BOOST_CHARCONV_HAS_FLOAT128 was defined in the sources only if BOOST_CHARCONV_HAS_QUADMATH, but was then used in header files in the public API, where the macro had no chance of being defined. This led to some of the __float128 overloads being incorrecly ifdef-ed out, even when quadmath is available.
• Since BOOST_CHARCONV_HAS_QUADMATH was not being propagated in the Jamfile, some tests were not being run and had missing includes. I think I got them right, but it'd be nice if you could review them.
• I've removed the requirement to link to quadmath in the test Jamfile, since this is now handled by the usage requirement. Note that this also causes the tests to run from CMake, since boost_test_jamfile only picks simple test lines.

[mborland]

• Note that the BOOST_CHARCONV_NO_QUADMATH CMake option is still valid and working. I've only removed the C++ macro definition it caused, as it's not used and doesn't have an equivalent in the Jamfile.
• BOOST_CHARCONV_HAS_FLOAT128 was defined in the sources only if BOOST_CHARCONV_HAS_QUADMATH, but was then used in header files in the public API, where the macro had no chance of being defined. This led to some of the __float128 overloads being incorrecly ifdef-ed out, even when quadmath is available.
• Since BOOST_CHARCONV_HAS_QUADMATH was not being propagated in the Jamfile, some tests were not being run and had missing includes. I think I got them right, but it'd be nice if you could review them.
• I've removed the requirement to link to quadmath in the test Jamfile, since this is now handled by the usage requirement. Note that this also causes the tests to run from CMake, since boost_test_jamfile only picks simple test lines.

Thanks for the run down. Your part looks good; I'll come behind and clean up newly exposed warnings/errors.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.85%. Comparing base (ffd3e71) to head (0cd42b7).
Report is 13 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #252   +/-   ##
========================================
  Coverage    94.85%   94.85%           
========================================
  Files           69       69           
  Lines         9085     9085           
========================================
  Hits          8618     8618           
  Misses         467      467           

Files with missing lines	Coverage Δ
include/boost/charconv/detail/buffer_sizing.hpp	100.00% <ø> (ø)
include/boost/charconv/detail/issignaling.hpp	100.00% <ø> (ø)
...lude/boost/charconv/detail/ryu/ryu_generic_128.hpp	92.72% <100.00%> (ø)
include/boost/charconv/from_chars.hpp	100.00% <ø> (ø)
src/to_chars_float_impl.hpp	83.39% <ø> (ø)
test/github_issue_110.cpp	100.00% <ø> (ø)
test/github_issue_152_float128.cpp	100.00% <ø> (ø)
test/test_128bit_emulation.cpp	100.00% <ø> (ø)
test/test_float128.cpp	100.00% <ø> (ø)

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