Illumos iconv_open does not support empty encoding, unlike Solaris 11 and Linux.
Ensure a fallback mechanism.

Not suitable for upstream

diff --git a/src/main/sysutils.c b/src/main/sysutils.c
index 1d10dae..6b3c5d1 100644
--- a/src/main/sysutils.c
+++ b/src/main/sysutils.c
@@ -1461,7 +1461,7 @@ static void *iconv_open_internal(const char *tocode, const char *fromcode)
 
 void * Riconv_open (const char* tocode, const char* fromcode)
 {
-#if defined Win32 || __APPLE__
+#if defined Win32 || __APPLE__ || __sun
 // These two support "utf8"
 # ifdef Win32
     const char *cp = "ASCII";