考虑下面的示例project_（CMakeLists.txt）：

cmake_minimum_required(VERSION 3.1)

project(CCL LANGUAGES C CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_C_STANDARD 99)
set(CMAKE_C_STANDARD_REQUIRED ON)

find_library(MATH_LIBRARY m)
add_executable(main main.cpp)
if (MATH_LIBRARY)
  target_link_libraries(main PUBLIC ${MATH_LIBRARIES})
endif()

#include <iostream>
#include <cmath>

Main.cpp:

int main(void)
{
    std::cout << "Hello, sin()" << std::sin(30) << std::endl;
    return 0;
}

我想用下面的CMake工具链（aarch 64-toolchain.cmake）编译这个项目：

# Cross-compilation system information.
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR aarch64)

# The sysroot contains all the libraries we might need to link against and
# possibly headers we need for compilation.
set(CMAKE_SYSROOT /var/lib/schroot/chroots/ubuntu-focal-arm64)
set(CMAKE_FIND_ROOT_PATH ${CMAKE_SYSROOT})
set(CMAKE_LIBRARY_ARCHITECTURE aarch64-linux-gnu)

# Install path when SYSROOT is read-only.
# set(CMAKE_STAGING_PREFIX aarch64-staging)

# Set the compilers for C, C++ and Fortran.
set(GCC_TRIPLE "aarch64-linux-gnu")
set(CMAKE_C_COMPILER ${GCC_TRIPLE}-gcc-10 CACHE FILEPATH "C compiler")
set(CMAKE_CXX_COMPILER ${GCC_TRIPLE}-g++-10 CACHE FILEPATH "C++ compiler")
set(CMAKE_Fortran_COMPILER ${GCC_TRIPLE}-gfortran CACHE FILEPATH "Fortran compiler")

# Automatically use the cross-wrapper for pkg-config when available.
set(PKG_CONFIG_EXECUTABLE aarch64-linux-gnu-pkg-config CACHE FILEPATH "pkg-config executable")

# Set the architecture-specific compiler flags.
set(ARCH_FLAGS "-mcpu=cortex-a53+crc+simd")
set(CMAKE_C_FLAGS_INIT ${ARCH_FLAGS})
set(CMAKE_CXX_FLAGS_INIT ${ARCH_FLAGS})
set(CMAKE_Fortran_FLAGS_INIT ${ARCH_FLAGS})

# Don't look for programs in the sysroot (these are ARM programs, they won't run
# on the build machine).
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# Only look for libraries, headers and packages in the sysroot, don't look on
# the build machine.
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

set(CPACK_DEBIAN_PACKAGE_ARCHITECTURE arm64)

其中系统根目录（/var/lib/schroot/chroots/ubuntu-focal-arm 64）是使用以下命令设置的：

name=ubuntu-focal
mk-sbuild --arch=arm64 --skip-proposed --skip-updates --skip-security --name=${name} focal
su - $USER
mk-sbuild --arch=arm64 --skip-proposed --skip-updates --skip-security --name=${name} focal

配置方面，这工作得很好，但是当我尝试“正确地”构建这个项目find_library时，发现错误的libm.so库：

$ cmake -DCMAKE_TOOLCHAIN_FILE=../aarch-toolchain.cmake ..
$ make
Scanning dependencies of target main
[ 50%] Building CXX object CMakeFiles/main.dir/main.cpp.o
make[2]: *** No rule to make target '/var/lib/schroot/chroots/ubuntu-focal-arm64/usr/lib/aarch64-linux-gnu/libm.so', needed by 'main'.  Stop.
make[1]: *** [CMakeFiles/Makefile2:76: CMakeFiles/main.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

查看sysroot本身，可以正确找到库，但很明显，它是指向sysroot本地文件的符号链接，而不是指向主机：

$ ls -hal /var/lib/schroot/chroots/ubuntu-focal-arm64/usr/lib/aarch64-linux-gnu/
lrwxrwxrwx  1 root root   32 Apr 14  2020 libm.so -> /lib/aarch64-linux-gnu/libm.so.6

在我看来，CMake选择了错误的库（find_library实际上应该先使用编译器库），所以我猜我的工具链文件写得不正确。应该如何修改它以正确地找到数学库，而不改变sysroot或项目本身？
(Also，请注意，这是一个示例项目来说明问题。我仍然需要能够搜索sysroot中的包。）

编辑

正如注解中所要求的，结束状态应该是一个正确的aarch 64二进制文件（“main”），本质上，下面的构建命令无论有没有工具链都应该成功，并且应该产生一个功能性的二进制文件（尽管aarch 64二进制文件自然只能在sysroot中工作）。

$ mkdir -p host-build && cd host-build && cmake .. && make 
$ mkdir -p device-build && cd device-build && cmake -DCMAKE_TOOLCHAIN_FILE=../aarch64-toolchain.cmake .. && make