[gspell] build: fix comment about symbol visibility handling

[Sébastien Wilmet <swilmet src gnome org>]

commit bdcfa9da55d9233e97e88fcd993f6f20378d6193
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Mon Apr 17 13:44:31 2017 +0200

    build: fix comment about symbol visibility handling

 configure.ac |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index b93e0e8..59fbdb2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -155,8 +155,11 @@ AX_CODE_COVERAGE
 AX_REQUIRE_DEFINED([AX_VALGRIND_CHECK])
 AX_VALGRIND_CHECK
 
-# Visibility handling
-# This requires that every gspell/*.c file #includes config.h.
+# Symbol visibility handling.
+#
+# This requires to #include config.h in every *.c file where there is a public
+# symbol. As a simpler rule, it's easier to #include config.h in all gspell/*.c
+# files, to be sure that we don't miss any public symbol.
 GSPELL_HIDDEN_VISIBILITY_CFLAGS=""
 case "$host" in
     *-*-mingw*)