Cross compile support for cpptools integration.

[bjosa]

Cross Compile support for cpptools integration

Added compile flags and sysroot to the compiler path for cpptools.

This change addresses [#637]

Generally all cross compiling toolchains that depend on special compiler flags and a sysroot. These flags have to be published to the cpptools compilePath option. The cpptools extension then parses the compiler with These flags for the right include paths and defines.

This changes cpptools integration

The following changes are proposed:

• Add compile flags to cpptools compilePath
• Add sysroot to cpptools compilePath

[bjosa]

Maybe related to #604, #599

[msftclas]

All CLA requirements met.

[icegood]

I don't get how to use it. Please, update official documentation. At least I don't see any way to set sysroot somewhere in options.

[bjosa]

Just provide a cmake-kits.json file with the specific settings for your toolchain. See the cmake-kits section of the documentation for more information.

Example cmake-kits entry with an CMake toolchain file. The CMake toolchain file of the sdk then defines the sysroot path and all neccessary compiler flags:

{
    "name": "arm-linux-gnueabihf",
    "toolchainFile": "/home/user/sdk/toolchain.cmake",
    "cmakeSettings": {
        "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
        "CMAKE_STAGING_PREFIX": "${workspaceFolder}/build/${buildKit}/out",
        "CMAKE_PREFIX_PATH": [
            "${workspaceFolder}/build/${buildKit}/out"
        ]
    },
    "preferredGenerator": {
        "name": "Ninja"
    }
}