on systems where long doubles are just doubles. FreeBSD hasn't
been such a system since it started using gcc-2.5 many years ago.
The fix is of low quality. It loses precision.
scanf() of long doubles doesn't seem to be used much, but gdb-4.16
uses %Lg format in its expression parser if it thinks that the
system supports printf'ing of long doubles. The symptom was that
floating point literals were usually interpreted to be 0.0.
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