9996 use GCC 7 as default primary compiler

*** 21,31 ****
  # Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  # Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
  # Copyright 2012 Joshua M. Clulow <josh@sysmgr.org>
  # Copyright 2015, OmniTI Computer Consulting, Inc. All rights reserved.
  # Copyright 2018 OmniOS Community Edition (OmniOSce) Association.
! # Copyright (c) 2019, Joyent, Inc.
  #
  # - This file is sourced by "bldenv.sh" and "nightly.sh" and should not
  #   be executed directly.
  # - This script is only interpreted by ksh93 and explicitly allows the
  #   use of ksh93 language extensions.
--- 21,31 ----
  # Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  # Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
  # Copyright 2012 Joshua M. Clulow <josh@sysmgr.org>
  # Copyright 2015, OmniTI Computer Consulting, Inc. All rights reserved.
  # Copyright 2018 OmniOS Community Edition (OmniOSce) Association.
! # Copyright 2019, Joyent, Inc.
  #
  # - This file is sourced by "bldenv.sh" and "nightly.sh" and should not
  #   be executed directly.
  # - This script is only interpreted by ksh93 and explicitly allows the
  #   use of ksh93 language extensions.
*** 76,87 ****
  # There can be several space-separated entries in SHADOW_* to run multiple
  # shadow compilers.
  #
  # To disable shadow compilation, unset SHADOW_* or set them to the empty string.
  #
! export SHADOW_CCS=gcc7,/usr/gcc/7/bin/gcc,gnu
! export SHADOW_CCCS=gcc7,/usr/gcc/7/bin/g++,gnu
  
  # uncomment to enable smatch
  #export ENABLE_SMATCH=1
  
  # Comment this out to disable support for SMB printing, i.e. if you
--- 76,90 ----
  # There can be several space-separated entries in SHADOW_* to run multiple
  # shadow compilers.
  #
  # To disable shadow compilation, unset SHADOW_* or set them to the empty string.
  #
! export GNUC_ROOT=/usr/gcc/7
! export PRIMARY_CCS=gcc7,$GNUC_ROOT/bin/gcc,gnu
! export PRIMARY_CCCS=gcc7,$GNUC_ROOT/bin/g++,gnu
! export SHADOW_CCS=gcc4,/opt/gcc/4.4.4/bin/gcc,gnu
! export SHADOW_CCCS=gcc4,/opt/gcc/4.4.4/bin/g++,gnu
  
  # uncomment to enable smatch
  #export ENABLE_SMATCH=1
  
  # Comment this out to disable support for SMB printing, i.e. if you