Folks,
this is basically the same issue as I reported in readline:
https://lists.gnu.org/archive/html/bug-readline/2021-08/msg00000.html
The bad hunk seems not to be POSIX shell compliant. Both vars are set
for me on HP-UX because the expansion is incomplete. According to [1] it
has to be $(GCC:+..} and not $(GCC+..}. I have changed ./configure
locally and it works with /bin/sh.
I assume that this should also work on any other POSIX compliant shell.
Michael
[1]
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02
