; INSTALL.REPO: Mention cases that 'make bootstrap' can't handle (Bug#26246).

INSTALL.REPO

@@ -50,8 +50,21 @@ To update loaddefs.el (and similar files), do:
   $ make autoloads
 
 If either of the above partial procedures fails, try 'make bootstrap'.
-If CPU time is not an issue, 'make bootstrap' is the most thorough way
-to rebuild, and avoid any spurious problems.
+If CPU time is not an issue, 'make bootstrap' is a more thorough way
+to rebuild, avoiding spurious problems.
+
+Occasionally, there are changes that 'make bootstrap' won't be able to
+handle.  The most thorough cleaning can be achieved by 'git clean -fx'
+which will leave you with only files from the git repository.  Here
+are some faster methods for a couple of particular error cases:
+
+    /usr/bin/m4:aclocal.m4:9: cannot open `m4/count-leading-zeros.m4': No such file or directory
+
+This can be fixed with 'rm aclocal.m4'.
+
+    make: *** No rule to make target 'lib/Makefile.am', needed by 'lib/Makefile.in'
+
+This can be fixed with 'rm lib/Makefile Makefile'.
 
 Because the repository version of Emacs is a work in progress, it will
 sometimes fail to build.  Please wait a day or so (and check the