[glib] meson: fix unit tests and "Invalid byte sequence in conversion input"

[Tim-Philipp Müller <tpm src gnome org>]

commit 2ac8079b9414be67a99f736e15383e85da56f7dd
Author: Tim-Philipp Müller <tim centricular com>
Date:   Wed Jul 19 10:34:45 2017 +0100

    meson: fix unit tests and "Invalid byte sequence in conversion input"
    
    Check if strerror_r returns a char * and define STRERROR_R_CHAR_P
    if so, which is needed by g_strerror() since c8e268b
    
    https://bugzilla.gnome.org/show_bug.cgi?id=784000

 config.h.meson |    3 +++
 meson.build    |   17 +++++++++++++++++
 2 files changed, 20 insertions(+), 0 deletions(-)
---
diff --git a/config.h.meson b/config.h.meson
index a3d090e..9be7901 100644
--- a/config.h.meson
+++ b/config.h.meson
@@ -398,6 +398,9 @@
 /* Define to 1 if you have the `strerror_r' function. */
 #mesondefine HAVE_STRERROR_R
 
+/* Define if strerror_r returns char * */
+#mesondefine STRERROR_R_CHAR_P
+
 /* Define to 1 if you have the <strings.h> header file. */
 #mesondefine HAVE_STRINGS_H
 
diff --git a/meson.build b/meson.build
index 8c82fb8..99afed0 100644
--- a/meson.build
+++ b/meson.build
@@ -339,6 +339,23 @@ foreach f : functions
   endif
 endforeach
 
+# Check whether strerror_r returns char *
+if have_func_strerror_r
+  if cc.compiles('''#define _GNU_SOURCE
+                    #include <string.h>
+                    int func (void) {
+                      char error_string[256];
+                      char *ptr = strerror_r (-2, error_string, 256);
+                      char c = *strerror_r (-2, error_string, 256);
+                      return c != 0 && ptr != (void*) 0L;
+                    }
+                 ''',
+                 name : 'strerror_r() returns char *')
+    glib_conf.set('STRERROR_R_CHAR_P', 1,
+                  description: 'Defined if strerror_r returns char *')
+  endif
+endif
+
 # Special-case these functions that have alternative names on Windows/MSVC
 if cc.has_function('snprintf') or cc.has_header_symbol('stdio.h', 'snprintf')
   glib_conf.set('HAVE_SNPRINTF', 1)