[llvm] [NFC] Eliminate top-level "using namespace" from some headers. (PR #102751)

[Rahul Joshi via llvm-commits]

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@@ -12,7 +12,7 @@
 #include "RISCVTargetStreamer.h"
 #include "llvm/MC/MCELFStreamer.h"
 
-using namespace llvm;
+namespace llvm {
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jurahul wrote:

Right, that's why the build is failing. Let me make sure all the backends this is touching build locally for me before making it ready for review again.

https://github.com/llvm/llvm-project/pull/102751