cygwin: Fix spkg-configure.m4 for iconv

[mkoeppe]

Follow-up from #27823 (spkg-configure.m4 for iconv), comment 46:

It seems that, at least on Cygwin, AM_ICONV will pass, somehow, even if iconv.h is installed, thus making the libicon-devel package on Cygwin a requirement, at least when it comes to building R (which otherwise fails at #include <iconv.h>).

For now I'll just update the Cygwin build instructions to require libiconv-devel as a prerequisite which is preferable anyways. But maybe this still needs to be checked for somehow...

Indeed this needs fixing:

configure:21635: g++ -std=gnu++11 -o conftest.exe -g -O2    conftest.cpp -lglpk -lreadline -lcurl -lbz2 -lflint -lmpfr -lgmp -lm  -lntl -liconv >&5
conftest.cpp:68:10: fatal error: iconv.h: No such file or directory
   68 | #include <iconv.h>
      |          ^~~~~~~~~
compilation terminated.
...

configure:21645: result: no, consider installing GNU libiconv
## ------------------------------------------------------ ##
## Checking whether SageMath should install SPKG iconv... ##
## ------------------------------------------------------ ##
configure:21940: will use system package and not install SPKG iconv
## ---------------------------------------------------- ##

CC: @embray @orlitzky @dimpase

Component: build: configure

Author: Matthias Koeppe

Branch/Commit: 49c8e4d

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29532

[dimpase]

comment:1

hmm, so you are not running ./bootstrap on Cygwin?

[dimpase]

comment:2

note that spkg-install says

    echo "iconv will be installed as the operating system is Cygwin, HP-UX or Solaris."
    echo "These systems either lack iconv, or do not have a sufficiently capable"

Is this no longer true for Cygwin?

[mkoeppe]

comment:3

Gettext is installed, bootstrap worked.

[mkoeppe]

Branch: u/mkoeppe/cygwin__fix_spkg_configure_m4_for_iconv

[mkoeppe]

New commits:

49c8e4d

build/pkgs/iconv/spkg-configure.m4: Fix quoting bug

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

Commit: 49c8e4d

[dimpase]

Reviewer: Dima Pasechnik

[dimpase]

comment:7

OK, good catch.

[mkoeppe]

comment:8

Thanks!

[vbraun]

Changed branch from u/mkoeppe/cygwin__fix_spkg_configure_m4_for_iconv to 49c8e4d