Portion of build output:

Making all in man
--- amdgpu.4x ---
/usr/bin/sed -e 's|__vendorversion__|"xlibre-xf86-video-amdgpu 25.0.1" "X Version 11"|'         -e 's|__xorgversion__|"xlibre-xf86-video-amdgpu 25.0.1" "X Version 11"|'      -e 's|__xservername__|Xorg|g'   -e 's|__xconfigfile__|xorg.conf|g'      -e 's|__projectroot__|/usr/local|g'     -e 's|__apploaddir__||g'     -e 's|__appmansuffix__|1|g'      -e 's|__drivermansuffix__|4x|g'         -e 's|__adminmansuffix__|8|g'   -e 's|__libmansuffix__|3|g'     -e 's|__miscmansuffix__|7|g'  -e 's|__filemansuffix__|5|g' < amdgpu.man > amdgpu.4x
Making all in conf
===>  Staging for xlibre-xf86-video-amdgpu-25.0.3_1
===>   xlibre-xf86-video-amdgpu-25.0.3_1 depends on file: /usr/local/libdata/pkgconfig/xi.pc - found
===>   xlibre-xf86-video-amdgpu-25.0.3_1 depends on file: /usr/local/libdata/pkgconfig/xorg-server.pc - found
===>   xlibre-xf86-video-amdgpu-25.0.3_1 depends on file: /usr/local/libdata/pkgconfig/xi.pc - found
===>   xlibre-xf86-video-amdgpu-25.0.3_1 depends on file: /usr/local/libdata/pkgconfig/xorg-server.pc - found
===>   Generating temporary packing list
if test -z 'strip'; then  /usr/bin/make  INSTALL_PROGRAM="/bin/sh /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/xf86-video-amdgpu-xlibre-xf86-video-amdgpu-25.0.3/install-sh -c -s"  install_sh_PROGRAM="/bin/sh /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/xf86-video-amdgpu-xlibre-xf86-video-amdgpu-25.0.3/install-sh -c -s" INSTALL_STRIP_FLAG=-s  install;  else  /usr/bin/make  INSTALL_PROGRAM="/bin/sh /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/xf86-video-amdgpu-xlibre-xf86-video-amdgpu-25.0.3/install-sh -c -s"  install_sh_PROGRAM="/bin/sh /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/xf86-video-amdgpu-xlibre-xf86-video-amdgpu-25.0.3/install-sh -c -s" INSTALL_STRIP_FLAG=-s  "INSTALL_PROGRAM_ENV=STRIPPROG='strip'" install;  fi
Making install in src
 /bin/mkdir -p '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/lib/xorg/modules/xlibre-25/drivers/video'
 /bin/sh ../libtool   --mode=install /usr/bin/install -c -s  amdgpu_drv.la '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/lib/xorg/modules/xlibre-25/drivers/video'
libtool: install: /usr/bin/install -c .libs/amdgpu_drv.so /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/lib/xorg/modules/xlibre-25/drivers/video/amdgpu_drv.so
libtool: install: strip --strip-unneeded /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/lib/xorg/modules/xlibre-25/drivers/video/amdgpu_drv.so
libtool: install: /usr/bin/install -c .libs/amdgpu_drv.lai /usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/lib/xorg/modules/xlibre-25/drivers/video/amdgpu_drv.la
libtool: warning: remember to run 'libtool --finish /usr/local/lib/xorg/modules/xlibre-25/drivers/video'
Making install in man
 /bin/mkdir -p '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/share/man/man4'
 install  -m 0644 amdgpu.4x '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/share/man/man4'
Making install in conf
 /bin/mkdir -p '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/share/X11/xorg.conf.d'
 install  -m 0644 10-amdgpu.conf '/usr/ports/x11-drivers/xlibre-xf86-video-amdgpu/work/stage/usr/local/share/X11/xorg.conf.d'
====> Compressing man pages (compress-man)
===>  Installing for xlibre-xf86-video-amdgpu-25.0.3_1
===>  Checking if xlibre-xf86-video-amdgpu is already installed
===>   Registering installation for xlibre-xf86-video-amdgpu-25.0.3_1 as automatic
Installing xlibre-xf86-video-amdgpu-25.0.3_1...
===>   xlibre-drivers-1.0_1 depends on file: /usr/local/lib/xorg/modules/xlibre-25//drivers/amdgpu_drv.so - not found
*** Error code 1

Stop.
make[1]: stopped making "/usr/ports/x11-drivers/xlibre-drivers/work/.install_done.xlibre-drivers._usr_local" in /usr/ports/x11-drivers/xlibre-drivers
*** Error code 1

Stop.
make: stopped making "install clean" in /usr/ports/x11-drivers/xlibre-drivers


The build also provides the install location but here is verification on my system:
root@ichigo:/usr/ports/x11-drivers/xlibre-drivers # ls /usr/local/lib/xorg/modules/xlibre-25//drivers
modesetting_drv.so video
root@ichigo:/usr/ports/x11-drivers/xlibre-drivers # ls /usr/local/lib/xorg/modules/xlibre-25/drivers/video
amdgpu_drv.so