Quote the first argument in each use of AC_DEFUN.

m4/c-bs-a.m4

@@ -1,8 +1,8 @@
-#serial 3
+#serial 4
 
 dnl From Paul Eggert.
 
-AC_DEFUN(AC_C_BACKSLASH_A,
+AC_DEFUN([AC_C_BACKSLASH_A],
 [
   AC_CACHE_CHECK([whether backslash-a works in strings], ac_cv_c_backslash_a,
    [AC_TRY_COMPILE([],