threads: add a thread_local autoconf check

configure.ac

@@ -659,6 +659,28 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
   ]
 )
 
+TEMP_LDFLAGS="$LDFLAGS"
+LDFLAGS="$TEMP_LDFLAGS $PTHREAD_CFLAGS"
+AC_MSG_CHECKING([for thread_local support])
+AC_LINK_IFELSE([AC_LANG_SOURCE([
+  #include <thread>
+  static thread_local int foo = 0;
+  static void run_thread() { foo++;}
+  int main(){
+  for(int i = 0; i < 10; i++) { std::thread(run_thread).detach();}
+  return foo;
+  }
+  ])],
+  [
+    AC_DEFINE(HAVE_THREAD_LOCAL,1,[Define if thread_local is supported.])
+    AC_MSG_RESULT(yes)
+  ],
+  [
+    AC_MSG_RESULT(no)
+  ]
+)
+LDFLAGS="$TEMP_LDFLAGS"
+
 # Check for different ways of gathering OS randomness
 AC_MSG_CHECKING(for Linux getrandom syscall)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>

src/sync.cpp

@@ -11,6 +11,9 @@
 #include <stdio.h>
 
 #ifdef DEBUG_LOCKCONTENTION
+#if !defined(HAVE_THREAD_LOCAL)
+static_assert(false, "thread_local is not supported");
+#endif
 void PrintLockContention(const char* pszName, const char* pszFile, int nLine)
 {
     LogPrintf("LOCKCONTENTION: %s\n", pszName);