druntime/dmain2: disable RTSan monitoring in init_rt ...

... this function is not real-time safe and also not rtsan safe (will
lock-up rtsan's stack scanner)

Author: liushuyu

runtime/druntime/src/ldc/sanitizers_optionally_linked.d

@@ -39,6 +39,9 @@ version (SupportSanitizers)
             void __sanitizer_finish_switch_fiber(void* fake_stack_save, const(void)** bottom_old, size_t* size_old);
             void* __asan_get_current_fake_stack();
             void* __asan_addr_is_in_fake_stack(void *fake_stack, void *addr, void **beg, void **end);
+            void __rtsan_disable();
+            void __rtsan_enable();
+            void __rtsan_notify_blocking_call(const(char)* name);
         });
     }
 
@@ -79,6 +82,30 @@ version (SupportSanitizers)
             return null;
     }
 
+    nothrow @nogc
+    void rtsanDisable()
+    {
+        auto fptr = getOptionalSanitizerFunc!"__rtsan_disable"();
+        if (fptr)
+            fptr();
+    }
+
+    nothrow @nogc
+    void rtsanEnable()
+    {
+        auto fptr = getOptionalSanitizerFunc!"__rtsan_enable"();
+        if (fptr)
+            fptr();
+    }
+
+    nothrow @nogc
+    void rtsanNotifyBlockingCall(const(char) *name)
+    {
+        auto fptr = getOptionalSanitizerFunc!"__rtsan_notify_blocking_call"();
+        if (fptr)
+            fptr(name);
+    }
+
     // This uses the forward declaration of `functionName` and returns a pointer to that function
     // if it is found in the executable, and `null` otherwise. Templated such that it can internally
     // cache the function pointer. Thread-safe.

runtime/druntime/src/rt/dmain2.d

@@ -103,6 +103,13 @@ private shared size_t _initCount;
  */
 extern (C) int rt_init()
 {
+    version (SupportSanitizers)
+    {
+        import ldc.sanitizers_optionally_linked;
+        rtsanNotifyBlockingCall("rt_init");
+        rtsanDisable();
+        scope (exit) rtsanEnable();
+    }
     /* @@BUG 11380 @@ Need to synchronize rt_init/rt_term calls for
        version (Shared) druntime, because multiple C threads might
        initialize different D libraries without knowing about the