[glib] meson: Fix error message for iconv detection

[Nirbheek Chauhan <nirbheekc src gnome org>]

commit ab0a0c706cfa8105a93972b3e31875af9bf77792
Author: Nirbheek Chauhan <nirbheek centricular com>
Date:   Wed May 16 14:26:11 2018 +0530

    meson: Fix error message for iconv detection

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 94922c334..7f017e613 100644
--- a/meson.build
+++ b/meson.build
@@ -1586,7 +1586,7 @@ else
   endif
 
   if not found_iconv
-    error('No iconv() implementation found in C library or libiconv')
+    error('iconv implementation "@0@" not found'.format(iconv_opt))
   endif
 
 endif