Prefix error messages with program name.

It make it easier while debugging to know who is reporting the error:
Ninja itself or one of the command called by Ninja during the build
process or one of the generator which called Ninja.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/util.h b/src/util.h
index 188528c..e697b92 100644
--- a/src/util.h
+++ b/src/util.h
@@ -19,3 +19,6 @@ void DumpBacktrace(int skip_frames);
 
 // Log a fatal message, dump a backtrace, and exit.
 void Fatal(const char* msg, ...);
+
+// Log an error message.
+void Error(const char* msg, ...);