I tried to compile proton from this repository on macOS Big Sur 12.1.

I did this ../proton/configure.sh with the following output:

:: No build name specified, using default: proton-localbuild
:: Making sure that the container engine is working.
../proton/configure.sh: line 24: -1: substring expression < 0
+ 
Unable to find image 'registry.gitlab.steamos.cloud/proton/soldier/sdk:0.20210505.0-2' locally
0.20210505.0-2: Pulling from proton/soldier/sdk
4baad5400e18: Pull complete 
cb992ad9adcc: Pull complete 
63e1e57bb194: Pull complete 
3c054042ceb7: Pull complete 
40fc2088ae6c: Pull complete 
4f7b3f14f416: Pull complete 
b42ab69b3c38: Pull complete 
9ae4481a79f3: Pull complete 
d6ba9ea939bf: Pull complete 
95aa240f1dbf: Pull complete 
9c11fc98d6c4: Pull complete 
665190e9ff79: Pull complete 
daddf6694cb6: Pull complete 
5ef637f5e151: Pull complete 
e79820cf4a20: Pull complete 
94475803dd2e: Pull complete 
5a3b0ac3ba33: Pull complete 
ffc44389ae50: Pull complete 
96e5021a7560: Pull complete 
91429e7039c9: Pull complete 
87d4aa91d011: Pull complete 
839331e0996b: Pull complete 
3946197437af: Pull complete 
Digest: sha256:004b04f0a73f7ad108b1515337d4d1eff2ff4e9dc34ade3102c719328ac37505
Status: Downloaded newer image for registry.gitlab.steamos.cloud/proton/soldier/sdk:0.20210505.0-2
:: Created ./Makefile, now run make to build.
::   See README.md for make targets and instructions

Then I tried to execute make, but I got this error:

/Applications/Xcode.app/Contents/Developer/usr/bin/make  -f Makefile NO_NESTED_MAKE=1
../proton/build/makefile_base.mak:116: *** multiple target patterns.  Stop.
make: *** [nested_make] Error 2

What did I wrong?