MFC r268232:
  The u-boot tarball needed for some boards, BEAGLEBONE for
  example, explicitly hard-code gcc(1) as the compiler.

  Partially revert r264703, which did a post-chroot install
  of gcc(1).  This was initially removed because gcc(1) fails
  to build usr.bin/dtc/ causing the xdev target to fail.  So
  this time, move the gcc(1) installation after xdev is built.

  This change is likely applicable to stable/10 arm build
  failures, as well.

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