Support build for powerpc

[axetroy]

https://github.com/axetroy/cask.rs/runs/5643148108?check_suite_focus=true

error: failed to run custom build command for `bzip2-sys v0.1.11+1.0.8`

Caused by:
  process didn't exit successfully: `/home/runner/work/cask.rs/cask.rs/target/release/build/bzip2-sys-a6ccc4bdf2d32a24/build-script-build` (exit status: 1)
  --- stdout
  cargo:rerun-if-env-changed=BZIP2_NO_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_powerpc64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS_powerpc64_unknown_linux_gnu
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_ALLOW_CROSS
  cargo:rerun-if-env-changed=PKG_CONFIG_powerpc64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_powerpc64_unknown_linux_gnu
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_powerpc64-unknown-linux-gnu
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_powerpc64_unknown_linux_gnu
  cargo:rerun-if-env-changed=TARGET_PKG_CONFIG_SYSROOT_DIR
  cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
  TARGET = Some("powerpc64-unknown-linux-gnu")
  OPT_LEVEL = Some("z")
  HOST = Some("x86_64-unknown-linux-gnu")
  CC_powerpc64-unknown-linux-gnu = None
  CC_powerpc64_unknown_linux_gnu = None
  TARGET_CC = None
  CC = None
  CROSS_COMPILE = None
  CFLAGS_powerpc64-unknown-linux-gnu = None
  CFLAGS_powerpc64_unknown_linux_gnu = None
  TARGET_CFLAGS = None
  CFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("false")
  CARGO_CFG_TARGET_FEATURE = None
  running: "powerpc-linux-gnu-gcc" "-Os" "-ffunction-sections" "-fdata-sections" "-fPIC" "-m64" "-I" "bzip2-1.0.8" "-D_FILE_OFFSET_BITS=64" "-DBZ_NO_STDIO" "-o" "/home/runner/work/cask.rs/cask.rs/target/powerpc64-unknown-linux-gnu/release/build/bzip2-sys-111e0700d8097fca/out/lib/bzip2-1.0.8/blocksort.o" "-c" "bzip2-1.0.8/blocksort.c"

  --- stderr

  error occurred: Failed to find tool. Is `powerpc-linux-gnu-gcc` installed?

remove bzip2-sys and use in pure-rust impl