Reland "[Support] Add a way to run a function on a detached thread""

This reverts commit 7bc7fe6b789d25d48d6dc71d533a411e9e981237.
The immediate callers have been fixed to pass nullopt where appropriate.

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Support/Unix/Unix.h b/llvm/lib/Support/Unix/Unix.h
index 86309b0567f..1fc9a414f74 100644
--- a/llvm/lib/Support/Unix/Unix.h
+++ b/llvm/lib/Support/Unix/Unix.h
@@ -21,6 +21,7 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Chrono.h"
 #include "llvm/Support/Errno.h"
+#include "llvm/Support/ErrorHandling.h"
 #include <algorithm>
 #include <assert.h>
 #include <cerrno>
@@ -69,6 +70,14 @@ static inline bool MakeErrMsg(
   return true;
 }
 
+// Include StrError(errnum) in a fatal error message.
+LLVM_ATTRIBUTE_NORETURN static inline void ReportErrnumFatal(const char *Msg,
+                                                             int errnum) {
+  std::string ErrMsg;
+  MakeErrMsg(&ErrMsg, Msg, errnum);
+  llvm::report_fatal_error(ErrMsg);
+}
+
 namespace llvm {
 namespace sys {