Unable to build against `clang:12`

[bartoszek]

I was trying to build cgrep-clang on Arch env:{llvm:12.0.0,clang:12.0.0} but it fails with:

clang++ -MM -fpic -I/usr/include -std=c++14   -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/build/llvm/src/llvm-12.0.0.src/tools/clang/include -I/usr/tools/clang/include -std=c++17 -fexceptions  cgrep.cpp > ./.depend
echo  cgrep.odbg: cgrep.cpp pch.hpp cfe-extra/cfe_extra.h | sed -r 's/[A-Za-z0-9\-\_]+\.odbg/\n&/g' >> ./.depend
echo  cgrep.ocov: cgrep.cpp pch.hpp cfe-extra/cfe_extra.h | sed -r 's/[A-Za-z0-9\-\_]+\.ocov/\n&/g' >> ./.depend
clang++ -fpic -I/usr/include -std=c++14   -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/build/llvm/src/llvm-12.0.0.src/tools/clang/include -I/usr/tools/clang/include -std=c++17 -fexceptions  -c pch.hpp -o pch.hpp.gch
clang++ -fpic -I/usr/include -std=c++14   -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/build/llvm/src/llvm-12.0.0.src/tools/clang/include -I/usr/tools/clang/include -std=c++17 -fexceptions  -c cfe-extra/cfe_extra.cpp -o cfe-extra/cfe_extra.o
clang++ -include-pch pch.hpp.gch -fpic -I/usr/include -std=c++14   -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/build/llvm/src/llvm-12.0.0.src/tools/clang/include -I/usr/tools/clang/include -std=c++17 -fexceptions  -c cgrep.cpp -o cgrep.o
cgrep.cpp:212:21: error: use of undeclared identifier 'ast_type_traits'
                    ast_type_traits::DynTypedNode &DTN) {
                    ^
cgrep.cpp:315:9: error: use of undeclared identifier 'ast_type_traits'
        ast_type_traits::DynTypedNode DNode =
        ^
cgrep.cpp:316:13: error: use of undeclared identifier 'ast_type_traits'
            ast_type_traits::DynTypedNode::create(*FD);

cgrep-clang-1.1-2-x86_64-build.log