From b0377f798f6794b6c93be150da6bc3fc140f1ce4 Mon Sep 17 00:00:00 2001
From: Tony Finch <fanf@isc.org>
Date: Wed, 15 Feb 2023 19:00:37 +0000
Subject: [PATCH] Avoid redefining _FORTIFY_SOURCE

Some compilers have a built-in definition of the _FORTIFY_SOURCE macro
that differs from BIND's preferred setting. This causes errors like
the one quoted below. The solution is to undefine the macro before
defining it. A similar fix was recently committed to glibc.

    <command line>: error: '_FORTIFY_SOURCE' macro redefined
    #define _FORTIFY_SOURCE 2
            ^
    <built-in>: note: previous definition is here
    #define _FORTIFY_SOURCE 0
	    ^

https://sourceware.org/git/glibc.git/commitdiff/35bcb08eaa953c9b
---
 configure.ac | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 4aa1761b26..c180364dfb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -134,8 +134,9 @@ STD_LDFLAGS=""
 # ... except in test code
 TEST_CFLAGS="-Wno-vla"
 
-# Fortify the sources by default
-STD_CPPFLAGS="-D_FORTIFY_SOURCE=2"
+# Fortify the sources by default (we undefine the macro first in case
+# the compiler has a different built-in setting)
+STD_CPPFLAGS="-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2"
 
 #
 # Additional compiler settings.