Relax COFF string table check

COFF object files with 0 as string table size are currently rejected. This
prevents us from reading object files written by tools like cvtres that
violate the PECOFF spec and write 0 instead of 4 for the size of an empty
string table.

llvm-svn: 202292
diff --git a/llvm/test/tools/llvm-readobj/coff-zero-string-table.test b/llvm/test/tools/llvm-readobj/coff-zero-string-table.test
new file mode 100644
index 0000000..dfcf79e
--- /dev/null
+++ b/llvm/test/tools/llvm-readobj/coff-zero-string-table.test
@@ -0,0 +1,8 @@
+Ensure that we can read COFF objects with a string table size of 0 (instead
+of 4) for empty string tables.
+
+RUN: llvm-readobj -t %p/Inputs/zero-string-table.obj.coff-i386 | FileCheck %s
+
+CHECK: Symbols [
+CHECK:   Symbol {
+CHECK:     Name: $R000000