Update test10 (it was a bit flaky), update libstdc++ binary, and added fake __libc_single_threadedhandling

src/wrapped/wrappedlibc.c

@@ -2726,6 +2726,9 @@ EXPORT char* my___progname_full = NULL;
 EXPORT char* my_program_invocation_name = NULL;
 EXPORT char* my_program_invocation_short_name = NULL;
 
+// ignoring this for now
+EXPORT char my___libc_single_threaded = 0;
+
 #define PRE_INIT\
     if(box64_tcmalloc_minimal)                                      \
         lib->priv.w.lib = dlopen(NULL, RTLD_LAZY | RTLD_GLOBAL);    \

src/wrapped/wrappedlibc_private.h

@@ -2301,4 +2301,6 @@ GOM(__deregister_frame_info, pFp)
 DATAM(program_invocation_name, sizeof(void*))
 DATAM(program_invocation_short_name, sizeof(void*))
 
+DATAM(__libc_single_threaded, 1)
+
 GO(iconvctl, iFlip)

tests/test10.cpp

@@ -11,6 +11,7 @@ std::stringstream stream;
 void append_number(int x) {
   while (lock_stream[x].load()) {}
   stream << "thread #" << x << '\n';
+  stream.flush();
   if (x != 9) lock_stream[x + 1].store(false);
 }