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

[Rahul Joshi via llvm-commits]

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@@ -20,17 +20,15 @@
 
 STATISTIC(NumPatternEmitted, "Number of patterns emitted");
 
-namespace llvm {
-namespace gi {
+using namespace llvm;
+using namespace gi;
 
-namespace {
-
-Error failUnsupported(const Twine &Reason) {
+static Error failUnsupported(const Twine &Reason) {
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jurahul wrote:

Added FIXME for future fixups.

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