message: Add include search path for cross targets on Linux
diff: @@ -158,13 +158,16 @@ function(builtin_to_cpp bit os_name arch supported_archs supported_oses resultFi
  # Determine triple
  set(fpic "")
  + set(debian_triple)
  if (${os_name} STREQUAL "windows")
  set(triple ${target_arch}-pc-win32)
  elseif (${os_name} STREQUAL "linux")
  if (${target_arch} STREQUAL "i686" OR ${target_arch} STREQUAL "x86_64" OR ${target_arch} STREQUAL "aarch64")
  set(triple ${target_arch}-unknown-linux-gnu)
  + set(debian_triple ${target_arch}-linux-gnu)
  elseif (${target_arch} STREQUAL "armv7")
  set(triple ${target_arch}-unknown-linux-gnueabihf)
  + set(debian_triple arm-linux-gnueabihf)
  else()
  message(FATAL_ERROR "Error")
  endif()
  @@ -225,6 +228,17 @@ function(builtin_to_cpp bit os_name arch supported_archs supported_oses resultFi
  if (${os_name} STREQUAL "macos")
  # -isystem/iusers/MacOSX10.14.sdk.tar/MacOSX10.14.sdk/usr/include
  set(includePath -isystem${ISPC_MACOS_SDK_PATH}/usr/include)
  + elseif(NOT ${debian_triple} STREQUAL "")
  + # When compiling on Linux, there are two way to support cross targets:
  + # - add "foreign" architecture to the set of supported architectures and install corresponding toolchain.
  + # For example on aarch64: "dpkg --add-architecture armhf" and "apt-get install libc6-dev:armhf".
  + # In this case the headers will be installed in /usr/include/arm-linux-gnueabihf and will be
  + # automatically picked up by clang.
  + # - install cross library. For example: "apt-get install libc6-dev-armhf-cross".
  + # In this case headers will be installed in /usr/arm-linux-gnueabihf/include and will not be picked up
  + # by clang by default. So the following line adds such path explicitly. If this path doesn't exist and
  + # the headers can be found in other locations, this should not be a problem.
  + set(includePath -isystem/usr/${debian_triple}/include)
  endif()
  endif()
  