[Concurrency] Avoid #include-ing dlfcn.h when not available (#41276)

Author: kubamracek

stdlib/public/Concurrency/AsyncLet.cpp

@@ -26,7 +26,7 @@
 #include "TaskPrivate.h"
 #include "Debug.h"
 
-#if !defined(_WIN32) && !defined(__wasi__)
+#if !defined(_WIN32) && !defined(__wasi__) && __has_include(<dlfcn.h>)
 #include <dlfcn.h>
 #endif
 

stdlib/public/Concurrency/Task.cpp

@@ -33,7 +33,7 @@
 #include <dispatch/dispatch.h>
 #endif
 
-#if !defined(_WIN32) && !defined(__wasi__)
+#if !defined(_WIN32) && !defined(__wasi__) && __has_include(<dlfcn.h>)
 #include <dlfcn.h>
 #endif
 

stdlib/public/Concurrency/TaskGroup.cpp

@@ -38,7 +38,7 @@
 #include <dispatch/dispatch.h>
 #endif
 
-#if !defined(_WIN32) && !defined(__wasi__)
+#if !defined(_WIN32) && !defined(__wasi__) && __has_include(<dlfcn.h>)
 #include <dlfcn.h>
 #endif
 

stdlib/public/Concurrency/ThreadSanitizer.cpp

@@ -17,7 +17,7 @@
 #include "TaskPrivate.h"
 
 // Thread Sanitizer is not supported on Windows or WASI.
-#if defined(_WIN32) || defined(__wasi__)
+#if defined(_WIN32) || defined(__wasi__) || !__has_include(<dlfcn.h>)
 void swift::_swift_tsan_acquire(void *addr) {}
 void swift::_swift_tsan_release(void *addr) {}
 #else