[MLIR] Avoid double space print on llvm global op

[bondhugula]

Summary

Fix extra space print for llvm global op when the 'unamed_addr'
attribute was empty. This led to two spaces being printed in the custom
form between non-whitespace chars. A round trip would add an extra space
to a typical spaced form. NFC.

[bondhugula]

Drop white space change to test case. Not really needed.

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

void GlobalOp::build(OpBuilder &builder, OperationState &result, Type type,
   if (addrSpace != 0)
     result.addAttribute("addr_space", builder.getI32IntegerAttr(addrSpace));
   result.attributes.append(attrs.begin(), attrs.end());
   result.addRegion();
 }
 
 static void printGlobalOp(OpAsmPrinter &p, GlobalOp op) {
   p << ' ' << stringifyLinkage(op.linkage()) << ' ';
-  if (op.unnamed_addr())
-    p << stringifyUnnamedAddr(*op.unnamed_addr()) << ' ';
+  if (auto unnamedAddr = op.unnamed_addr()) {
+    StringRef str = stringifyUnnamedAddr(*unnamedAddr);
+    if (!str.empty())
+      p << str << ' ';
+  }
   if (op.constant())
     p << "constant ";
   p.printSymbolName(op.sym_name());
   p << '(';
   if (auto value = op.getValueOrNull())
     p.printAttribute(value);
   p << ')';
   // Note that the alignment attribute is printed using the