My build and bootstrap test script. this does a ubsan bootstrap (to test __bdos with itself), x86_64 bootstrap and test, i686 build and test and a few cross build targets to generate a cc1 for quick testing.

build-worktree2.sh

#!/bin/bash

worktree_root=$HOME/src/upstream/gcc/

if [ -z $1 ]; then
  echo "Usage: $0 <git commit ref> [targets]"
  exit 1
fi
ref=$1
shift

if [ -z $1 ]; then
  targets="i686 x86_64 ubsan"
else
  targets="$@"
fi

LANGUAGES="--enable-languages=c,c++,fortran,lto"
COMMON_CONFIG_FLAGS="$LANGUAGES --enable-sanitizers --enable-shared --with-system-zlib"

cross_config() {
  target=$1
  if [ "x$1" = "xppc64le" ]; then
    build_target="powerpc64le-linux-gnu"
  else
    build_target="$target-linux-gnu"
  fi

  sysroot="/usr/$target-redhat-linux/sys-root/fc42"
  echo "--enable-languages=c,c++ --includedir=$sysroot/usr/include --libdir=$sysroot/usr/lib64 --with-build-sysroot=$sysroot/ --target=$build_target --disable-bootstrap --disable-libsanitizer --disable-multilib"
}

get_configure_flags() {
  case "$target" in
    i686)
      echo "$COMMON_CONFIG_FLAGS i686-linux --with-fpmath=sse --disable-bootstrap"
      ;;
    cross-*)
      cross_config $(echo $target | sed 's/cross-//')
      ;;
    ubsan)
      echo "$COMMON_CONFIG_FLAGS --with-build-config=bootstrap-ubsan --disable-multilib"
      ;;
    *)
      echo "$COMMON_CONFIG_FLAGS --enable-bootstrap"
      ;;
  esac
}

make_args() {
  target=$1
  case "$target" in
    cross-*)
      echo "SUBDIRS=gcc"
      ;;
    *)
      echo ""
      ;;
  esac
}

skip_test() {
  target=$1
  case "$target" in
    ubsan)
      echo true
      ;;
    cross-*)
      echo true
      ;;
    *)
      echo false
      ;;
  esac
}

if [ ! -d gcc-$ref ]; then
  echo "Worktree gcc-$ref not set up yet. Do that first."
  exit 1
fi

build_one() {
  target=$1
  ../configure $(get_configure_flags $target) > build.log 2>&1 && \
    make -j$(nproc) $(make_args) >> build.log 2>&1
  if [ $? -ne 0 ]; then
    echo "Build for $target failed, see $PWD/build.log for details"
    return
  fi
  if $(skip_test $target); then
    echo "skipping tests for $target"
  else
    echo "running tests for $target"
    make -j$(nproc) check > /dev/null 2>&1
    echo "Copying over test results for $target"
    mkdir -p $worktree_root/testresults/$ref
    find gcc/testsuite -name "*.log" | while read f; do
      cp -f $f $worktree_root/testresults/$ref/
    done
  fi
  echo "$target done"
}

build_target() {
  target=$1
  builddir=build-$target
  rm -rf $builddir
  mkdir $builddir

  pushd $builddir
  echo "Building for $target"
  time build_one $target
  popd # $builddir
}

pushd gcc-$ref
# Get the actual branch name.  For 15 for example, it'll be releases/gcc-15.
ref=$(git branch --show-current)
git remote update -p
if git branch -a | grep remotes/origin/$ref; then
  base=$ref
else
  # Jiska koi baap nahi hota, uska baap bhagvaan hota hai...
  base="master"
fi
git rebase origin/$base
# Sync with my github.  It's my github and not a canonical source of truth for
# anybody, so force rewriting is OK.
git push github +$ref
for t in $targets; do
  build_target $t
done
wait # wait for all builds to finish
popd # gcc-$ref