The problem is that configure seems to think that there *is* support
"long double math": the test succeeds and HAVE_ASINL (and all other
double math) is defined. So both compile and link appear to be succesful
as far as configure is concerned.
Before choosing a solution, I want to understand why the problem is
occuring.
According to the cited mail however, that is because configure checks
the availibility of "long double math" with a short piece of code,
supplying *it's own* function definition (and not using e.g. math.h) and
linking with *some* libraries. Because I do not understand how configure
is doing that (I have looked into the macros but failed to understand
them), I do not know what exactly the code is configure is using or to
which libraries configure links the executable. I think btw that it is
using libstdc++:
$ objdump.exe -t libstdc++.a | grep asinl
[ 2](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x00000020 _asinl