Use clang/LLVM toolchain with gcc stdlib to cross compile aarch64 target.

v3:
Removed AARCH_GCC and AARCH_CLANG variables in favor of CC_FOR_BUILD.

v4:
Rebased.
Updated commit msg in build: add aarch64 clang to meson cross-compile.

Juraj Linkeš (3):
  build: add aarch64 clang to meson cross-compile
  ci: add aarch64 clang cross-compilation builds
  doc: add clang to aarch64 cross build guide

 .ci/linux-build.sh                            |   6 +-
 .travis.yml                                   |  18 ++
 config/arm/arm64_armv8_linux_clang_ubuntu1804 |  20 ++
 .../linux_gsg/cross_build_dpdk_for_arm64.rst  | 183 +++++++++++++-----
 4 files changed, 175 insertions(+), 52 deletions(-)
 create mode 100644 config/arm/arm64_armv8_linux_clang_ubuntu1804

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2.20.1