mac下pip install 安装出错 error: command '/usr/bin/clang++'

building '_pywrapfst' extension
creating build/temp.macosx-11.1-arm64-cpython-39/extensions
clang++ -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -fwrapv -O2 -Wall -fPIC -O2 -isystem /opt/anaconda3/envs/megatts3-env/include -arch arm64 -I/opt/anaconda3/envs/megatts3-env/include -fPIC -O2 -isystem /opt/anaconda3/envs/megatts3-env/include -arch arm64 -I/opt/anaconda3/envs/megatts3-env/include/python3.9 -c extensions/_pywrapfst.cpp -o build/temp.macosx-11.1-arm64-cpython-39/extensions/_pywrapfst.o -std=c++17 -Wno-register -Wno-deprecated-declarations -Wno-unused-function -Wno-unused-local-typedefs -funsigned-char -stdlib=libc++ -mmacosx-version-min=10.12
extensions/_pywrapfst.cpp:1291:10: fatal error: 'fst/util.h' file not found
1291 | #include
| ^~~~~~~~~~~~
1 error generated.
error: command '/usr/bin/clang++' failed with exit code 1
[end of output]

note: This error originates from a subprocess, and is likely not a problem with pip.
ERROR: Failed building wheel for pynini
Failed to build pynini
ERROR: Failed to build installable wheels for some pyproject.toml based projects (pynini)

Reproduce the pynini installation on macOS arm64 with Python 3.9 and inspect the build of extensions/_pywrapfst.cpp. Start with the missing fst/util.h error and determine why the required header is unavailable during compilation. Done means pip can build and install pynini successfully in the reported environment.

Written by the indexing model from the issue text.