[issue33512] use more standard approach for detecting long double in configure

[Eitan Adler]

New submission from Eitan Adler <lists at eitanadler.com>:

autotools has a standard macro for defining HAVE_LONG_DOUBLE. Lets use it rather than using our own.

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components: Build
messages: 316615
nosy: eitan.adler
priority: normal
severity: normal
status: open
title: use more standard approach for detecting long double in configure

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33512>
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