Add DISABLE_MKSTEMP_DEFINE support

This macro as written won't compile on mingw32 due to the attributes
on _mktemp().  This could be worked around, but it's easier to just
disable it since I don't need it, and nobody else is building with
mingw32.
14 jobs for dailybuild_linux-x64 in 9 minutes and 28 seconds (queued for 14 seconds)
Status Job ID Name Coverage
  Build
passed #31286
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jsdoor-freebsd

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jsdoor-linux

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jsdoor-windows

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sbbs-freebsd

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sbbs-linux

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sbbs-windows

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sexpots-freebsd

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sexpots-linux

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sexpots-windows

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syncdraw-freebsd

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syncdraw-linux

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syncterm-freebsd

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syncterm-linux

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passed #31283
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syncterm-windows

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