[XRay] Adjust includes of bitset (NFC)

BlockVerifier.cpp uses std::bitset, not BlockVerifier.h.

Identified with clangd.

Author: kazutakahirata

llvm/include/llvm/XRay/BlockVerifier.h

@@ -14,7 +14,6 @@
 #define LLVM_XRAY_BLOCKVERIFIER_H
 
 #include "llvm/XRay/FDRRecords.h"
-#include <bitset>
 
 namespace llvm {
 namespace xray {

llvm/lib/XRay/BlockVerifier.cpp

@@ -8,6 +8,8 @@
 #include "llvm/XRay/BlockVerifier.h"
 #include "llvm/Support/Error.h"
 
+#include <bitset>
+
 namespace llvm {
 namespace xray {
 namespace {