我的问题通过 回复 我的错误报告，但我在此处添加了答案，以便将所有信息集中在一处以供将来参考.

My question was answered through the reply to my bug report, but I add the answer here to have all information in one place for future reference.

简而言之:如果您从 llvm.org.如果您想使用 clang/clang++ 接口(这是为 ARM 交叉编译所必需的)，您必须通过 msys2 安装 Clang.

In short: CMake currently does not support to use the clang/clang++ command line interface if you install Clang from llvm.org. If you want to use the clang/clang++ interface (which is necessary to cross-compile for ARM) you have to install Clang via msys2.

详细

Windows 上的 Clang 有两个不同的命令行界面:

Clang on Windows has two different command line interfaces:

• clang/clang++ 试图成为的默认界面与 GCCs gcc/g++ 兼容并针对 GNU ABI
• clang-cl 试图与微软的 Visual C++ 兼容编译器 cl.exe 并针对 MSVC ABI

• clang/clang++ the default interface that attempts to be compatible with GCCs gcc/g++ and targets the GNU ABI
• clang-cl that attempts to be compatible with Microsofts Visual C++ compiler cl.exe and targets the MSVC ABI

为了对 ARM 进行交叉编译，您需要 clang/clang++ 接口.问题是 CMake 支持不同的接口，具体取决于您安装 Clang 的方式(请参阅 bug在 CMake 问题跟踪器中了解更多详细信息):

In order to cross-compile for ARM you need the clang/clang++ interface. The Problem is CMake supports different interfaces depending on how you installed Clang (see the bug in the CMake issue tracker for more details):

• 如果您从 llvm.org 安装 Clang，则 CMake 仅支持 clang-cl 接口.
• 如果您通过 msys2 安装 Clang，则 CMake 支持 clang/clang++ 接口.

• If you install Clang from llvm.org CMake only supports the clang-cl interface.
• If you install Clang via msys2 CMake supports the clang/clang++ interface.

这就是我所做的:

1. 安装msys2
2. 使用 pacman 安装 Clang 和 CMake.msys2中有两个clang包，一个mingw32和一个mingw64版本.我使用了 mingw64 包 (mingw-w64-x86_64-clang).
3. 启动 mingw64 shell 并运行 CMake 并从那里构建.

1. Install msys2
2. Install Clang and CMake with pacman. There are two clang packages in msys2, a mingw32 and a mingw64 version. I used the mingw64 package (mingw-w64-x86_64-clang).
3. Launch the mingw64 shell and run CMake and build from there.

工具链文件

我的原始工具链文件有两个问题花了我很长时间才修复.所以我希望这会为其他人节省一些时间:

There were two problems with my original toolchain file that took my a long time to fix. So I hope this will save others some time:

1. 目标三元组(例如 arm-none-eabi)需要匹配 GCC binutils 的前缀完全.我的 binutils 的前缀是 arm-none-eabi(例如 arm-none-eabi-ar)，所以我不得不相应地更改目标三元组.
2. CMAKE_TRY_COMPILE_TARGET_TYPE 需要更改为 STATIC_LIBRARY 才能防止 CMake 在编译检查期间运行链接器.

1. The target triple (e.g. arm-none-eabi) needs to match the prefix of the GCC binutils exactly. The prefix of my binutils was arm-none-eabi (e.g. arm-none-eabi-ar) so I had to change the target triple accordingly.
2. CMAKE_TRY_COMPILE_TARGET_TYPE needs to be changed to STATIC_LIBRARY in order to prevent CMake from running the linker during the compile check.

这是我使用的最终工具链文件(您还可以在此GitHub 存储库):

Here is the final toolchain file I used (you can also find a good example for a toolchain file in this GitHub repo):

cmake_minimum_required(VERSION 3.13)

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR ARM)

if(DEFINED ENV{GCC_ARM_TOOLCHAIN})
    set(GCC_ARM_TOOLCHAIN $ENV{GCC_ARM_TOOLCHAIN})
else()
    set(GCC_ARM_TOOLCHAIN "C:/Users/user/tools/gcc-arm-none-eabi-7-2018-q2-update-win32")
endif()

LIST(APPEND CMAKE_PROGRAM_PATH ${GCC_ARM_TOOLCHAIN})

# Specify the cross compiler
# The target triple needs to match the prefix of the binutils exactly
# (e.g. CMake looks for arm-none-eabi-ar)
set(CLANG_TARGET_TRIPLE arm-none-eabi)
set(GCC_ARM_TOOLCHAIN_PREFIX ${CLANG_CLANG_TARGET_TRIPLE})
set(CMAKE_C_COMPILER clang)
set(CMAKE_C_COMPILER_TARGET ${CLANG_TARGET_TRIPLE})
set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_COMPILER_TARGET ${CLANG_TARGET_TRIPLE})
set(CMAKE_ASM_COMPILER clang)
set(CMAKE_ASM_COMPILER_TARGET ${CLANG_TARGET_TRIPLE})

# Don't run the linker on compiler check
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)

# Specify compiler flags
set(ARCH_FLAGS "-mcpu=cortex-a5 -mthumb -mfpu=neon-vfpv4 -mfloat-abi=hard -mno-unaligned-access")
set(CMAKE_C_FLAGS "-Wall ${ARCH_FLAGS}" CACHE STRING "Common flags for C compiler")
set(CMAKE_CXX_FLAGS "-Wall -std=c++17 -fno-exceptions -fno-rtti -fno-threadsafe-statics ${ARCH_FLAGS}" CACHE STRING "Common flags for C++ compiler")
set(CMAKE_ASM_FLAGS "-Wall ${ARCH_FLAGS} -x assembler-with-cpp" CACHE STRING "Common flags for assembler")
set(CMAKE_EXE_LINKER_FLAGS "-nostartfiles -Wl,-Map,kernel.map,--gc-sections -fuse-linker-plugin -Wl,--use-blx --specs=nano.specs --specs=nosys.specs" CACHE STRING "")

# C/C++ toolchain
set(GCC_ARM_SYSROOT "${GCC_ARM_TOOLCHAIN}/${GCC_ARM_TOOLCHAIN_PREFIX}")
# set(CMAKE_SYSROOT ${GCC_ARM_SYSROOT})
set(CMAKE_FIND_ROOT_PATH ${GCC_ARM_SYSROOT})

# Search for programs in the build host directories
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
# For libraries and headers in the target directories
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)