I am cross compiling to ARM using the g++ 7.2 compilers provided with the Xilinx SDK.
This compiler was built using old assumptions about system headers being pure C, such that when compiled from a .cpp source, the header is wrapped in an `extern "C" {}`. This causes true C++ headers to fail when compiling templates, with 'error: template with C linkage'. I have filed a bug against the ARM gcc compiler, but I would like to be able to workaround the bug with CMake if possible. And as I read the documentation, I am beginning to think that there may be a bug in CMake too. As I read the documentation for target_include_directories, the `-isystem` option for specifying an include directory is triggered by the SYSTEM option, and therefore should not be used when SYSTEM is not specified. But it seems to me that `-isystem` may be used even if SYSTEM is not specified. For example, the yaml-cpp <https://github.com/jbeder/yaml-cpp> project declares its include directories like this: if (NOT CMAKE_VERSION VERSION_LESS 2.8.12) target_include_directories(yaml-cpp PUBLIC $<BUILD_INTERFACE:${YAML_CPP_SOURCE_DIR}/include> $<INSTALL_INTERFACE:${INCLUDE_INSTALL_ROOT_DIR}> PRIVATE $<BUILD_INTERFACE:${YAML_CPP_SOURCE_DIR}/src>) endif() But if I make a trivial project that simply includes yaml-cpp as a dependency, the generated compile commands use `-isystem` to include the yaml-cpp headers. Is this a bug in CMake? Also, is there any way I may be able to work around this problem with CMake 3.10? I would be happy to globally force the use of `-I` for all include directories. Thanks, Jim Lloyd EtaGen Inc.
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