Syntax error while building proton

Proton Version: commit 80d70143334871c29474eb0c329e6eb52e8c396b (HEAD -> proton_5.0, tag: proton-5.0-5b

I tried to install proton on my Ubuntu 19.10. The steam runtime was installed successfully but the compilation of proton failed. I am using fish shell but I tried to execute it in a bash environment and it still didn't work.

I followed the build instructions as follows

• Dependencies installed
• Repo cloned
• Steam runtime installed

$ docker images
REPOSITORY           TAG                 IMAGE ID            CREATED             SIZE
steam-proton-dev32   latest              7d00136e9605        3 days ago          1.94GB
steam-proton-dev     latest              36c2b334e51a        3 days ago          2.11GB
hello-world          latest              fce289e99eb9        15 months ago       1.84kB
$

$ mkdir proton-mybuild
$ cd proton-mybuild
$ ../proton/configure.sh --steam-runtime64=docker:steam-proton-dev --steam-runtime32=docker:steam-proton-dev32 --steam-runtime=$HOME/steam-runtime/runtime/ --build-name="proton-mybuild"
:: Configuring with build name: proton-mybuild
:: Created ./Makefile, now run make to build.
::   See README.md for make targets and instructions
$

$ make
[...]
checking whether build environment is sane... yes
checking whether make sets $(MAKE)... yes
checking whether make supports the include directive... yes (GNU style)
checking whether make supports nested variables... yes
checking dependency style of gcc... gcc3
checking whether to enable maintainer-specific portions of Makefiles... yes
checking whether make supports nested variables... (cached) yes
/home/giosuel/proton/vkd3d/configure: line 5411: syntax error near unexpected token `2.4.2'
/home/giosuel/proton/vkd3d/configure: line 5411: `LT_PREREQ(2.4.2)'
make[1]: *** [../proton/build/makefile_base.mak:1671: obj-vkd3d32/Makefile] Error 2
make[1]: Leaving directory '/home/giosuel/proton-mybuild'
make: *** [../proton/build/makefile_base.mak:17: nested_make] Error 2
$

OS: Ubuntu 19.10
GNOME Shell 3.34.3
sh: fish, version 3.0.2

The failure is reported in vkd3d/configure at line 5411 after configure.sh creates the build; start by reproducing with the shown Docker runtime arguments and make command, then inspect the generated configure input around LT_PREREQ(2.4.2). Done means the Proton build proceeds past this syntax error.