Starting from gstreamer 1.20.3 
I ran
meson -Dgpl=enabled -Dugly=enabled -Dgst-plugins-ugly:x264=enabled builddir
Afterwards: ninja -C builddir
That one fails at : I think it links to the libx264.a file, while I want it to link to the libx264.so sharewd lib.
FAILED: subprojects/gst-plugins-ugly/ext/x264/libgstx264.so
cc -o subprojects/gst-plugins-ugly/ext/x264/libgstx264.so subprojects/gst-plugins-ugly/ext/x264/libgstx264.so.p/gstx264enc.c.o subprojects/gst-plugins-ugly/ext/x264/libgstx264.so.p/gstencoderbitrateprofilemanager.c.o -Wl,–as-needed -Wl,–no-undefined -shared -fPIC -Wl,–start-group -Wl,-soname,libgstx264.so -Wl,-Bsymbolic-functions ‘-Wl,-rpath,$ORIGIN/…/…/…/gstreamer/libs/gst/base:$ORIGIN/…/…/…/gstreamer/gst:$ORIGIN/…/…/…/gst-plugins-base/gst-libs/gst/video:$ORIGIN/…/…/…/orc/orc:$ORIGIN/…/…/…/gst-plugins-base/gst-libs/gst/pbutils:$ORIGIN/…/…/…/gst-plugins-base/gst-libs/gst/audio:$ORIGIN/…/…/…/gst-plugins-base/gst-libs/gst/tag’ -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gstreamer/libs/gst/base -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gstreamer/gst -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gst-plugins-base/gst-libs/gst/video -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/orc/orc -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gst-plugins-base/gst-libs/gst/pbutils -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gst-plugins-base/gst-libs/gst/audio -Wl,-rpath-link,/home/gstreamer-1.20.3/builddir/subprojects/gst-plugins-base/gst-libs/gst/tag subprojects/gstreamer/libs/gst/base/libgstbase-1.0.so.0.2003.0 subprojects/gstreamer/gst/libgstreamer-1.0.so.0.2003.0 subprojects/gst-plugins-base/gst-libs/gst/video/libgstvideo-1.0.so.0.2003.0 subprojects/orc/orc/liborc-0.4.so.0.32.0 subprojects/gst-plugins-base/gst-libs/gst/pbutils/libgstpbutils-1.0.so.0.2003.0 subprojects/gst-plugins-base/gst-libs/gst/audio/libgstaudio-1.0.so.0.2003.0 subprojects/gst-plugins-base/gst-libs/gst/tag/libgsttag-1.0.so.0.2003.0 /usr/lib/x86_64-linux-gnu/libglib-2.0.so /usr/lib/x86_64-linux-gnu/libgobject-2.0.so -Wl,–export-dynamic /usr/lib/x86_64-linux-gnu/libgmodule-2.0.so -pthread -lm /usr/lib/x86_64-linux-gnu/libz.so -lx264 -Wl,–end-group
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/11/…/…/…/x86_64-linux-gnu/libx264.a(base.o): warning: relocation against stderr@@GLIBC_2.2.5' in read-only section .text’
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/11/…/…/…/x86_64-linux-gnu/libx264.a(base.o): relocation R_X86_64_PC32 against symbol `stderr@@GLIBC_2.2.5’ can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value