[llvm-readobj] Install llvm-readelf alias

Install an llvm-readelf symlink to llvm-readobj.
When invoked as *readelf*, default to -elf-output-style=GNU.

Patch by Roland McGrath

Differential Revision: https://reviews.llvm.org/D33869

llvm-svn: 308408
diff --git a/llvm/tools/llvm-readobj/llvm-readobj.cpp b/llvm/tools/llvm-readobj/llvm-readobj.cpp
index 3aa79541..7bfb18f 100644
--- a/llvm/tools/llvm-readobj/llvm-readobj.cpp
+++ b/llvm/tools/llvm-readobj/llvm-readobj.cpp
@@ -34,6 +34,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/Signals.h"
@@ -544,7 +545,8 @@
 }
 
 int main(int argc, const char *argv[]) {
-  sys::PrintStackTraceOnErrorSignal(argv[0]);
+  StringRef ToolName = argv[0];
+  sys::PrintStackTraceOnErrorSignal(ToolName);
   PrettyStackTraceProgram X(argc, argv);
   llvm_shutdown_obj Y;
 
@@ -553,6 +555,9 @@
 
   opts::WideOutput.setHiddenFlag(cl::Hidden);
 
+  if (sys::path::stem(ToolName).find("readelf") != StringRef::npos)
+    opts::Output = opts::GNU;
+
   cl::ParseCommandLineOptions(argc, argv, "LLVM Object Reader\n");
 
   // Default to stdin if no filename is specified.