build errors with `_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`

构建输出指出了 src/helpers/buffer.cpp，并显示使用 clang 和 libc++ 编译时，第 87 行和第 137 行缺少 std::string 声明。首先阅读该文件的 include，以及项目针对 _LIBCPP_REMOVE_TRANSITIVE_INCLUDES 选项的构建配置。使用该选项后，报告中的构建成功即表示完成；issue 还建议考虑添加一个 CI job。

FYI, there are some missing includes that are revealed with clang + libc++. It's not too big of a problem, but it might be useful to fix / add ci job.

FAILED: [code=1] src/libpisp.so.1.7.0.p/helpers_buffer.cpp.o 
/usr/bin/ccache clang++ -Isrc/libpisp.so.1.7.0.p -Isrc -I../src -Isrc/libpisp -I../src/libpisp -I/usr/include -fdiagnostics-color=always -D_GLIBCXX_ASSERTIONS=1 -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -D_GLIBCXX_DEBUG=1 -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG -std=c++20 -O0 -g -DPISP_LOGGING_ENABLE=1 -DBOOST_BIND_GLOBAL_PLACEHOLDERS -Wno-address-of-packed-member -stdlib=libc++ -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -fPIC -pthread -DBOOST_LOG_DYN_LINK=1 -DBOOST_LOG_SETUP_DYN_LINK=1 -DBOOST_THREAD_BUILD_DLL=1 -DBOOST_THREAD_USE_DLL=1 -DBOOST_ALL_NO_LIB -MD -MQ src/libpisp.so.1.7.0.p/helpers_buffer.cpp.o -MF src/libpisp.so.1.7.0.p/helpers_buffer.cpp.o.d -o src/libpisp.so.1.7.0.p/helpers_buffer.cpp.o -c ../src/helpers/buffer.cpp
../src/helpers/buffer.cpp:87:52: error: implicit instantiation of undefined template 'std::basic_string<char>'
   87 |                         throw std::runtime_error("Unable to dup fd: " + std::string(strerror(errno)));
      |                                                                         ^
/usr/bin/../include/c++/v1/__fwd/string.h:43:7: note: template is declared here
   43 | class basic_string;
      |       ^
../src/helpers/buffer.cpp:87:50: error: invalid operands to binary expression ('const char[19]' and 'std::string' (aka 'basic_string<char>'))
   87 |                         throw std::runtime_error("Unable to dup fd: " + std::string(strerror(errno)));
      |                                                  ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../include/c++/v1/__iterator/reverse_iterator.h:293:1: note: candidate template ignored: could not match 'reverse_iterator' against 'basic_string'
  293 | operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x) {
      | ^
../src/helpers/buffer.cpp:137:52: error: implicit instantiation of undefined template 'std::basic_string<char>'
  137 |                         throw std::runtime_error("Unable to dup fd: " + std::string(strerror(errno)));
      |                                                                         ^
/usr/bin/../include/c++/v1/__fwd/string.h:43:7: note: template is declared here
   43 | class basic_string;
      |       ^
../src/helpers/buffer.cpp:137:50: error: invalid operands to binary expression ('const char[19]' and 'std::string' (aka 'basic_string<char>'))
  137 |                         throw std::runtime_error("Unable to dup fd: " + std::string(strerror(errno)));
      |                                                  ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../include/c++/v1/__iterator/reverse_iterator.h:293:1: note: candidate template ignored: could not match 'reverse_iterator' against 'basic_string'
  293 | operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x) {
      | ^
4 errors generated.