Merge from origin/emacs-27

a3c2d186eb (origin/emacs-27) CC Mode: Fix the handling of two adjacen...
a1abf73c76 Fix combine-change-calls-1 for when buffer-undo-list is t
db37dd2e84 Don't misinterpret doc string as initial value
40b217c2bf Bump checkdoc-version to match library header
60418a1ab2 Explain how to unset mode bindings (Bug#39802)
7cafbbe964 Fix describe-variable on values with circular syntax (Bug#...
592b1cfee9 Improve documentation of next-error-highlight-no-select (b...

diff --cc doc/emacs/building.texi
Simple merge

diff --cc lisp/help-fns.el
Simple merge

diff --cc lisp/progmodes/cc-mode.el
Simple merge

diff --cc lisp/progmodes/vhdl-mode.el
Simple merge

diff --cc lisp/simple.el
Simple merge

diff --cc lisp/subr.el
Simple merge