Portable Object Compiler builds on OmniOS r151056 with gcc 14.3. Also cursel builds and works ok on OmniOS.
add SUSE SLES 16.0 to Platforms.txt
The openSUSE rpm for Tumbleweed x86_64 also installs on SUSE SLES 16.0. The compiler 3.4.11 builds on SLES 16 with gcc 15.1.1 on the Linux 6.12.0 kernel. Cursel 1.1.3 runs on SLES 16 with ncurses 6.5 version 20250531 in console mode (TERM=linux).
I've placed binaries objc-3.4.11-1.i586.rpm and objc-3.4.10-1.x86_64.rpm for openSUSE Tumbleweed with Linux kernel 6.17.6-1 and gcc 15.2.1 using automake 1.18, autoconf 2.72 and byacc 20241231 in the openSUSE folder at https://sourceforge.net/projects/objc/files/opensuse/. The amd64 64bit rpm also installs on openSUSE Leap 16, it seems.
For me cursel 1.1.3 runs fine on openSUSE Tumbleweed with gcc 15.2.1 and Portable Object Compiler 3.4.11 (both AMD64 and Intel i586). Some new options are ./configure --without-ncursesw or --with-ncurses. Is the SLES15 system - where you said you installed objc-3.3.16-1.x86_64 and objc-3.4.3-1.x86_64 rpms, is it please under support from SUSE ? If you have a subscription (to get updates via "zypper"), perhaps best check with SUSE before changing anything, but in theory I think it would be useful...
add -bdwgc option
run autoupdate on configure.in
change library link order in Makefile