Comment # 1 on bug 1214288 from Richard Biener

There is no compiler that fully supports C++20 yet, that support is still
experimental and incomplete.  Definitely GCC 10 isn't supported for this.
Oddly enough even though you install gcc12 it's gcc10 that's being used.
When I execute the offending compiler command in the chroot and using
/usr/bin/g++12 instead of /usr/bin/g++10 the failure goes away.

So something is wrong with your setup of the compilers.  I see

[   29s] + export CXX=g++-12
[   29s] + CXX=g++-12
[   29s] + cmake -DCMAKE_BUILD_TYPE:STRING=RelWithDebInfo
-DCMAKE_INSTALL_PREFIX:STRING=/usr -DCMAKE_MESSAGE_LOG_LEVEL:STRING=STATUS -S .
-B build -GNinja -DCMAKE_C_COMPILER:STRING=gcc-10
-DCMAKE_CXX_COMPILER:STRING=g++-10 

^^^

and

build/CMakeCache.txt:CMAKE_CXX_COMPILER:STRING=/usr/bin/g++-10
build/DartConfiguration.tcl:BuildName: Linux-g++-10
build/DartConfiguration.tcl:Compiler: /usr/bin/g++-10

no idea where that's injected from.

GCC 10 isn't going to be fixed.