[llvm] [NFC][TableGen] Fix GlobalISel TableGen backend namespace usage (PR #156986)

[Rahul Joshi via llvm-commits]

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@@ -9,15 +9,13 @@
 #include "CombinerUtils.h"
 #include "llvm/ADT/StringSet.h"
 
-namespace llvm {
+using namespace llvm;
 
-StringRef insertStrRef(StringRef S) {
+StringRef llvm::insertStrRef(StringRef S) {
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jurahul wrote:

Added FIXME for future fixups.

https://github.com/llvm/llvm-project/pull/156986