[PATCH] strerror_r-posix: Fix override of AC_FUNC_STRERROR_R

[Eric Blake]

Requiring autoconf's AC_FUNC_STRERROR_R and then calling AC_DEFINE
ourselves leads to two insertions of #define STRERROR_R_CHAR_P
in confdefs.h, but with different values (at least on glibc).  This
in turn sparks a gcc warning about redeclaring the macro, and kills
any subsequent tests that use -Werror (which now error because of
the conflicting define, whether or not the test used to error).

A better approach is to replace the autoconf macro with a version
of our own that doesn't probe anything, so that the AC_DEFINE is
reached exactly once.

* m4/strerror_r.m4 (AC_FUNC_STRERROR_R): New override.
(gl_FUNC_STRERROR_R): Don't reuse AC_DEFINE() with a potentially
different value.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog        |  7 +++++++
 m4/strerror_r.m4 | 13 ++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e5d7987..4837fe2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2016-11-04  Eric Blake  <address@hidden>
+
+       strerror_r-posix: Fix override of AC_FUNC_STRERROR_R
+       * m4/strerror_r.m4 (AC_FUNC_STRERROR_R): New override.
+       (gl_FUNC_STRERROR_R): Don't reuse AC_DEFINE() with a potentially
+       different value.
+
 2016-11-03  Eric Blake  <address@hidden>

        bootstrap: Fix get_version() for AIX 5.3
diff --git a/m4/strerror_r.m4 b/m4/strerror_r.m4
index 06c51e1..c566f38 100644
--- a/m4/strerror_r.m4
+++ b/m4/strerror_r.m4
@@ -1,4 +1,4 @@
-# strerror_r.m4 serial 16
+# strerror_r.m4 serial 17
 dnl Copyright (C) 2002, 2007-2016 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -41,8 +41,15 @@ AC_DEFUN([gl_FUNC_STRERROR_R],

   # Overwrite the findings of AC_FUNC_STRERROR_R (for code that uses that).
   AC_REQUIRE([AC_FUNC_STRERROR_R])
-  AC_DEFINE([HAVE_DECL_STRERROR_R], [1])
-  AC_DEFINE([STRERROR_R_CHAR_P], [0])
+])
+
+# If this module is in use, we unconditionally want POSIX semantics; so
+# replace autoconf's macro with a version that does not probe
+AC_DEFUN([AC_FUNC_STRERROR_R], [
+  AC_DEFINE([HAVE_DECL_STRERROR_R], [1],
+    [Define to 1, since you should have the declaration of strerror_r.])
+  AC_DEFINE([STRERROR_R_CHAR_P], [0],
+    [Define to 0, since strerror_r should not return char *.])
 ])

 # Prerequisites of lib/strerror_r.c.
-- 
2.7.4