Can't build hello world without gcc instalation on linux got: We don't know how to get the definition of mbstate_t on your

I try to build simple hello world completely without gcc/g++ instalation just to use latest clang++-21.1.3.
hello.cxx:

#include

int main(int argc, char** argv)
{
std::cout << "hello world" << std::endl;
return std::cout.fail();
}

Command to build:

clang++ -std=c++20 -Wfatal-errors -stdlib=libc++ \
-isystem /home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1 \
-isystem /home/leo/LLVM-21.1.3-Linux-X64/include/x86_64-unknown-linux-gnu/c++/v1 \
hello.cxx

Output:

In file included from hello.cxx:1:
In file included from /home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1/iostream:45:
In file included from /home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1/ios:222:
In file included from /home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1/iosfwd:120:
In file included from /home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1/__std_mbstate_t.h:14:
/home/leo/LLVM-21.1.3-Linux-X64/include/c++/v1/__mbstate_t.h:51:4: fatal error: "We don't know how to get the
definition of mbstate_t on your platform."
51 | # error "We don't know how to get the definition of mbstate_t on your platform."
| ^
1 error generated.

I think it should be possible to build binary without instalation gcc toolchain just using [llvm release](https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.3/LLVM-21.1.3-Linux-X64.tar.xz)

Reproduce the reported command with the LLVM-21.1.3-Linux-X64 release and inspect the libc++ headers at include/c++/v1/__mbstate_t.h and __std_mbstate_t.h. Compare the platform setup used by the release with the missing mbstate_t definition; done means the cause and supported resolution for building without an installed GCC toolchain are established.

Written by the indexing model from the issue text.