./Modules/posixmodule.c:8436:15: error: implicit declaration of function 'sendfile' is invalid in C99 [-Werror,-Wimplicit-function-declaration] ret = sendfile(in, out, offset, &sbytes, &sf, flags);

こんなエラーで困っていた。

python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.7.5.tar.xz...
-> https://www.python.org/ftp/python/3.7.5/Python-3.7.5.tar.xz
Installing Python-3.7.5...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 11.4 using python-build 2.0.3-6-gf043f47c)

Inspect or clean up the working tree at /var/folders/v5/8bfg75xs40zgwf4wf12xyxtw0000gn/T/python-build.20210721153303.49986
Results logged to /var/folders/v5/8bfg75xs40zgwf4wf12xyxtw0000gn/T/python-build.20210721153303.49986.log

Last 10 log lines:
                                                     ^
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include   -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include   -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration   -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/keiichi/.pyenv/versions/3.7.5/include  -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/keiichi/.pyenv/versions/3.7.5/include   -DPy_BUILD_CORE_BUILTIN  -DPy_BUILD_CORE -c ./Modules/posixmodule.c -o Modules/posixmodule.o
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include   -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include   -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration   -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/keiichi/.pyenv/versions/3.7.5/include  -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/keiichi/.pyenv/versions/3.7.5/include   -DPy_BUILD_CORE_BUILTIN  -c ./Modules/errnomodule.c -o Modules/errnomodule.o
./Modules/posixmodule.c:8436:15: error: implicit declaration of function 'sendfile' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        ret = sendfile(in, out, offset, &sbytes, &sf, flags);
              ^
1 error generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....
1 warning generated.

bashでこれを打つとインストールされた。
fishだと打てないので気をつける

CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(
brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" pyenv install --patch 3.7.5 < <(curl -sSL https://github.com/python/cpython/commit/8ea6353.patch\?full_index\=1)