notice: if you are cross build, please follow step
----
define SRC_DIR you sdk root dir
SRC_DIR=$($READLINK -f "`dirname $0`")
source $SRC_DIR/megbrain/scripts/cmake-build/utils/utils.sh
build_flatc $SRC_DIR/megbrain false

your build code
----

GitOrigin-RevId: ad97860f5ffc1128a8c177f0822c02e240634716

GitOrigin-RevId: ccff72e39a4cd79f4cad0fbb474680a300204301

GitOrigin-RevId: 78b50a4f3a4fd0b762d39a91259f34e72997d04a

GitOrigin-RevId: d60c4052c1ac1c4f2b9879c60069d232c8efcd13

1: fix cmake cross-ios failed caused by df118a87
   build static lib for APPLE define for XCODE third_party framework including require

2: megbrain_test/megdnn_test build when MGE_INFERENCE_ONLY=ON
   now u can build megbrain_test/megdnn_test by:
   EXTRA_CMAKE_ARGS="-DMGE_WITH_TEST=ON" ./scripts/cmake-build/xxx.sh
   example macos-cross-ios build megdnn_test for IOS by
   EXTRA_CMAKE_ARGS="-DMGE_WITH_TEST=ON" ./scripts/cmake-build/cross_build_ios_arm_inference.sh

3: reuse host flatc build when cross build mode
GitOrigin-RevId: 132f4bf893567bdb1d54de506449950513a5841f

GitOrigin-RevId: 7ffd9b95416d629442c9ab9e0a79fcf2ac2cac42

host build and cross build

now cmake status:
a: host build
    1: windows build -- ok
    2: linux build -- ok
    3: macos build -- ok
b: cross build
    1: windows cross build arm-android -- ok
    2: windows cross build arm-linux   -- ok
    3: linux cross build arm-android -- ok
    4: linux cross build arm-linux   -- ok
    5: macos cross build arm-android -- ok
    6: macos cross build arm-linux   -- ok
    7: macos cross build ios         -- ok
GitOrigin-RevId: f7f376fe8c522410568c304a62310df823c70b65