obj2yaml: Improve error reporting

Previously only the error codes were reported which
meant that useful information about malformed inputs
was not shown.

Differential Revision: https://reviews.llvm.org/D34008

llvm-svn: 305609
diff --git a/llvm/test/Object/obj2yaml.test b/llvm/test/Object/obj2yaml.test
index 171488d..b89311d 100644
--- a/llvm/test/Object/obj2yaml.test
+++ b/llvm/test/Object/obj2yaml.test
@@ -478,4 +478,4 @@
 ELF-X86-64-UNWIND-NEXT:   Content:         ''
 
 RUN: not obj2yaml %t.blah 2>&1 | FileCheck --check-prefix=ENOENT %s
-ENOENT: Error: '{{[Nn]}}o such file or directory'
+ENOENT: Error reading file: {{.*}}.blah: {{[Nn]}}o such file or directory