The configure script checks that the compiler can build c programs and fails saying the compiler for c cannot build executables. (checking whether the C compiler works... no)
doing the command gcc x.c gives "gcc: error trying to exec 'cc1': execvp: No such file or directory"
uname -a for my system says: x86_64 x86_64 x86_64 GNU/Linux
My guess is that this version of GNAT was not configured correctly for c programs. Next thing to try is an older version of GNAT
The INSTALL file should give some additional info (in particular the last line, in case you have multiple versions of GNAT installed). Using GNAT CE 2019 installed on Debian 10 (Buster):
$ uname -a
Linux debian 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u1 (2019-09-20) x86_64 GNU/Linux
$ which gcc
/opt/GNAT/2019/bin/gcc
$ sudo apt-get install autoconf automake libtool
[...]
$ git clone https://github.com/AdaCore/PolyORB.git
[...]
$ cd PolyORB
$ support/reconfig
Running aclocal (GNU automake) 1.16.1
Running autoheader (GNU Autoconf) 2.69
Running autoconf (GNU Autoconf) 2.69
Generating IDL tree accessors
splitting nodes.ada into:
idl_fe-tree.ads
idl_fe-tree.adb
Doing the necessary date modifications
$ ./configure
[...]
checking whether the C compiler works... yes
[...]
$ make
[...]
