This worked for me:

$ git checkout v5.28.0
$ git clean -dxf
$ sh Configure -des -U d_strtod
$ grep -E '^d_strtod\b' config.sh
d_strtod='undef'
$ grep -E '#define.+HAS_STRTOD\b' config.h
/*#define HAS_STRTOD    / **/
$ make
$ ./perl -Ilib -MConfig -le 'print $Config{d_strtod}//"undef"'
undef

[download]

Another method is to patch config.sh (I've assumed you don't want d_strtod_l either):

$ sh Configure -des
$ perl -i.bak -pe "s/^d_strtod(?:_l)?=\K.*$/'undef'/" config.sh
$ sh Configure -S
$ make
# etc.

[download]

In reply to Re: Configuring perl such that HAS_STRTOD is not defined by haukex
in thread Configuring perl such that HAS_STRTOD is not defined by syphilis

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