[compiler-rt] [msan] Support POSIX iconv(3) on NetBSD 9.99.17+

Fixes build of test.

Author: krytarowski

compiler-rt/test/msan/iconv.cpp

@@ -8,14 +8,23 @@
 #include <stdio.h>
 #include <errno.h>
 
+#if defined(__NetBSD__)
+#include <sys/param.h>
+#if __NetBSD_Prereq__(9,99,17)
+#define NETBSD_POSIX_ICONV 1
+#else
+#define NETBSD_POSIX_ICONV 0
+#endif
+#endif
+
 int main(void) {
   iconv_t cd = iconv_open("ASCII", "ASCII");
   assert(cd != (iconv_t)-1);
 
   char inbuf_[100];
   strcpy(inbuf_, "sample text");
   char outbuf_[100];
-#if defined(__NetBSD__)
+#if defined(__NetBSD__) && !NETBSD_POSIX_ICONV
   // Some OSes expect the 2nd argument of iconv(3) to be of type const char **
   const char *inbuf = inbuf_;
 #else