[lld] Move handling of message separator to reportDiagnostic()

This ensures that it is also updated when calling log() and not just for
errors and warnings. This was noticed in the downstream CHERI fork where
a test using CHECK-NEXT was seeing empty lines after single-line log()
messages.

Reviewed By: MaskRay

Pull Request: #117587

Author: arichardson

lld/Common/ErrorHandler.cpp

@@ -219,6 +219,9 @@ void ErrorHandler::reportDiagnostic(StringRef location, Colors c,
   }
   os << msg << '\n';
   errs() << buf;
+  // If msg contains a newline, ensure that the next diagnostic is preceded by
+  // a blank line separator.
+  sep = getSeparator(msg);
 }
 
 void ErrorHandler::log(const Twine &msg) {
@@ -247,7 +250,6 @@ void ErrorHandler::warn(const Twine &msg) {
 
   std::lock_guard<std::mutex> lock(mu);
   reportDiagnostic(getLocation(msg), Colors::MAGENTA, "warning", msg);
-  sep = getSeparator(msg);
 }
 
 void ErrorHandler::error(const Twine &msg) {
@@ -278,7 +280,6 @@ void ErrorHandler::error(const Twine &msg) {
       exit = exitEarly;
     }
 
-    sep = getSeparator(msg);
     ++errorCount;
   }