CROSS_COMPILE_COMPAT cherry picks for linux-5.10.y and linux-5.15.y

Dear stable kernel maintainers,

Please consider cherry-picking to linux-5.15.y:

commit 3e6f8d1fa184 ("arm64: vdso32: require CROSS_COMPILE_COMPAT for gcc+bfd")

Please also consider cherry-picking to linux-5.10.y:

commit ef94340583ee ("arm64: vdso32: drop -no-integrated-as flag")
commit 3e6f8d1fa184 ("arm64: vdso32: require CROSS_COMPILE_COMPAT for gcc+bfd")

They landed in v5.13-rc1 and v5.16-rc1 respectively.

They allow the command line for building the arm64 compat vdso to be
shortened by dropping the need for CROSS_COMPILE_COMPAT for LLVM=1
(and LLVM_IAS=1) builds.

linux-5.15.y:
from:
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
to:
$ ARCH=arm64 make LLVM=1 -j72

linux-5.10.y:
from:
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 LLVM_IAS=1 -j72
to
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make LLVM=1 LLVM_IAS=1 -j72

This can be verified with the above by checking .config for
CONFIG_COMPAT_VDSO=y after running defconfig or building
arch/arm64/kernel/vdso32/.

I also verified these build with clang-10, which was the minimum
supported release of clang for linux-5.10.y and linux-5.15.y
(Documentation/process/changes.rst).
--
Thanks,
~Nick Desaulniers