maint: Use consistent coding style for build helper shell scripts * mk-octave-config-h.sh: Keep if-then on a single line. * move-if-change: Insert a space in interpreter directive for consistency. * build-env-features.sh, config-images.sh, config-module.sh, config-ops.sh, find-defun-files.sh, find-files-with-tests.sh, mk-errno-list, libinterp/mk-pkg-add, scripts/mk-pkg-add, mkbuiltins, mkdefs, mkdocs, mkf77def.in, mkops: Initialize environment variable defaults consistently. Use shift only when the argument list is not empty. Remove unnecessary quotes and semicolons on variable assignments. Insert/remove blank lines for consistency.

gnulib-hg = gnulib-hg