Default strip-commands assume a bash shell

I see in my logs:

[--:--:--] STATUS  [core/glib-networking.bst]: Running strip-commands

    find "/buildstream/install" -type f \
      '(' -perm -111 -o -name '*.so*' \
          -o -name '*.cmxs' -o -name '*.node' ')' \
      -exec sh -ec \
      'read -n4 hdr <"$1" # check for elf header
       if [ "$hdr" != "$(printf \\x7fELF)" ]; then
           exit 0
       fi
       debugfile="/buildstream/install/usr/lib/debug/$(basename "$1")"
       mkdir -p "$(dirname "$debugfile")"
       objcopy --only-keep-debug --compress-debug-sections "$1" "$debugfile"
       chmod 644 "$debugfile"
       strip --remove-section=.comment --remove-section=.note --strip-unneeded "$1"
       objcopy --add-gnu-debuglink "$debugfile" "$1"' - {} ';'
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n
-: 1: read: Illegal option -n

Looks like the problem is this line: 'read -n4 hdr <"$1" # check for elf header