Currently linktime-gc is enabled only on Linux s390x by default.
See
https://github.com/openjdk/jdk/blob/94a34a32aa723e4620f4ef4700b3e20d6ab9bf62/make/autoconf/jdk-options.m4#L106

We should enable it on Linux ppc64le too, to get smaller JDK native libs.
(please take into account that on Linux ppc64le, linktime-gc is only set for the JDK native libs, not for libjvm.so, because of still present issues with the serviceability agent)

Not all JDK native libs change a lot in lib size when enabling linktime-gc, but some shrink significantly, here are some good examples
gcc14 devkit linuxppc64le, product build jdk27
(normal => with ltgc)
708 K => 500 K images/jdk/lib/liblcms.so
476 K => 300 K images/jdk/lib/libsaproc.so
788 K => 720 K images/jdk/lib/libmlib_image.so
708 K => 500 K images/jdk/lib/liblcms.so
2476 K => 1476 K images/jdk/lib/libfontmanager.so