[llvm-exegesis] Move namespace exegesis inside llvm::

Summary:
This allows simplifying references of llvm::foo with foo when the needs
come in the future.

Reviewers: courbet, gchatelet

Reviewed By: gchatelet

Subscribers: javed.absar, tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D53455

llvm-svn: 344922
diff --git a/llvm/tools/llvm-exegesis/lib/Assembler.h b/llvm/tools/llvm-exegesis/lib/Assembler.h
index f2a7716..ee6bc86 100644
--- a/llvm/tools/llvm-exegesis/lib/Assembler.h
+++ b/llvm/tools/llvm-exegesis/lib/Assembler.h
@@ -32,6 +32,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
 
+namespace llvm {
 namespace exegesis {
 
 class ExegesisTarget;
@@ -82,5 +83,6 @@
 };
 
 } // namespace exegesis
+} // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_ASSEMBLER_H