[llvm-dev] Problem compiling the latest LLVM

[맹기완 via llvm-dev]

Hi, I am trying to build the latest LLVM and am seeing an error. I think it
is related to the new C++20, but am not sure.

Below is my cmake command. I am trying to compile for ARM:

cmake -G "Unix Makefiles" -DCMAKE_CROSSCOMPILING=True
-DLLVM_OPTIMIZED_TABLEGEN=1 -DCMAKE_BUILD_TYPE=Release
-DLLVM_TARGETS_TO_BUILD=ARM -DLLVM_TARGET_ARCH=ARMV7EM
-DLLVM_DEFAULT_TARGET_TRIPLE=armv7em-none-eabihf
-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi;compiler-rt;lld"
-DCMAKE_LINKER=/usr/bin/ld.gold -DCMAKE_INSTALL_PREFIX=../llvm-install/
../llvm-src/llvm/

I am getting the following error:
/home/kmaeng/llvm-build/include/c++/v1/__compare/compare_three_way_result.h:28:45:
error: expected primary-expression before ‘>’ token
   28 |   declval<__make_const_lvalue_ref<_Tp>>() <=>
declval<__make_const_lvalue_ref<_Up>>(), void()

I am suspecting it is something related to the new three way comparison but
cannot figure out how to fix it.
My cmake version is 3.16.3 and my g++ version is 9.3.0. I am using Ubuntu.

If you have any ideas or suggestions, it would be highly appreciated.

Thank you,
Best regards,
Kiwan Maeng
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