"no system package could be used" error for giac, but it is installed

edit

I am trying to build sagemath sage-9.8.rc0 on my Linux virtual box. I already have giac build and installed on the system, and have exported GIAC to point to it as well.

But when I run

 unset SAGE_ROOT
 unset SAGE_LOCAL
 export GIAC=/usr/local/bin/giac
 export MAXIMA=/usr/local/bin/maxima

./configure --with-system-python=no --with-system-giac=force

it gives error

configure: error: 

Given --with-system-giac=force, but no system package could be used.
That's an error.  Please install the indicated package to continue.
(To override this error, use ./configure --without-system-giac)

You see, I have it installed already

>which giac
/usr/local/bin/giac
>giac --version
// Using locale /usr/local/share/locale/
// en_US.utf8
// /usr/local/share/locale/
// giac
// UTF-8
// Maximum number of parallel threads 8
// (c) 2001, 2021 B. Parisse & others
1.9.0
>echo $GIAC
/usr/local/bin/giac
>

In addition to all of this, it wants me install giac using

 $ sudo pacman -S  eclib fflas-ffpack libgiac giac linbox

But I have already the latest giac compiled and build manually and installed as you see. If I do the above it will break things and might install giac version which is not what I want.

How do I tell sagemath not to install giac and use the system already installed one? Why does it not see it is installed in /usr/local/bin/giac ?

Update

The config.log file is located in this folder