From f329bba244264fb5f2c952c11e614987519d0dbc Mon Sep 17 00:00:00 2001
From: Tim Ruffing <crypto@timruffing.de>
Date: Mon, 1 Feb 2021 22:54:09 +0100
Subject: [PATCH] build: Add workaround for automake 1.13 and older

Fixes #890.
---
 configure.ac | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/configure.ac b/configure.ac
index 451915c..fd15d34 100644
--- a/configure.ac
+++ b/configure.ac
@@ -23,7 +23,15 @@ AC_PATH_TOOL(AR, ar)
 AC_PATH_TOOL(RANLIB, ranlib)
 AC_PATH_TOOL(STRIP, strip)
 
+# Save definition of AC_PROG_CC because AM_PROG_CC_C_O in automake<=1.13 will
+# redefine AC_PROG_CC to exit with an error, which avoids the user calling it
+# accidently and screwing up the effect of AM_PROG_CC_C_O. However, we'll need
+# AC_PROG_CC later on in AX_PROG_CC_FOR_BUILD, where its usage is fine, and
+# we'll carefully make sure not to call AC_PROG_CC anywhere else.
+m4_copy([AC_PROG_CC], [saved_AC_PROG_CC])
 AM_PROG_CC_C_O
+# Restore AC_PROG_CC
+m4_rename_force([saved_AC_PROG_CC], [AC_PROG_CC])
 
 AC_PROG_CC_C89
 if test x"$ac_cv_prog_cc_c89" = x"no"; then