Merge branch 'selftest/bpf, riscv: Improved cross-building support'

Björn Töpel says:

====================
From: Björn Töpel <bjorn@rivosinc.com>

Yet another "more cross-building support for RISC-V" series.

An example how to invoke a gen_tar build:

  | make ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- CC=riscv64-linux-gnu-gcc \
  |    HOSTCC=gcc O=/workspace/kbuild FORMAT= \
  |    SKIP_TARGETS="arm64 ia64 powerpc sparc64 x86 sgx" -j $(($(nproc)-1)) \
  |    -C tools/testing/selftests gen_tar

Björn
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>