Fix unresolved linker symbols from misplaced extern definitions

[chuckatkins]

Summary

When LCSSAID and LoopSimplifyID are declared extern inside a function body,
some linkers will fail to resolve the actual symbnols defined in the llvm
namespace. By removing the function local extern declarations and relying
on the header definitions in Scalar.h, the symbols can be properly reolved.
This is specifically an issue when building with the Intel compiler.

[chuckatkins]

Fix unresolved linker symbols from un-namespaced extern definitions

When LCSSAID and LoopSimplifyID are declared extern inside a function body,
some linkers will fail to resolve the actual symbols defined in the llvm
namespace. By removing the function local extern declarations and moving
them to outside the function body, the symbols can be properly resolved.
This is specifically an issue when building with the Intel compiler.

[majnemer]

lib/Transforms/Utils/LoopUtils.cpp

934–938

Please clang-format this.

[chuckatkins]

Adjusted code style with clang-format

[majnemer]

LGTM

lib/Transforms/Utils/LoopUtils.cpp

for (auto &Inst : *Block) {
             return !L->contains(Use->getParent());
           }))
         UsedOutside.push_back(&Inst);
     }
 
   return UsedOutside;
 }
 
+// We locally access their IDs for LoopSimplify and LCSSA here because
+// users shouldn't directly get them from this header.
+namespace llvm {
+extern char &LoopSimplifyID;
+extern char &LCSSAID;
+}
+
 void llvm::getLoopAnalysisUsage(AnalysisUsage &AU) {
   // By definition, all loop passes need the LoopInfo analysis and the
   // Dominator tree it depends on. Because they all participate in the loop
   // pass manager, they must also preserve these.
   AU.addRequired<DominatorTreeWrapperPass>();
   AU.addPreserved<DominatorTreeWrapperPass>();
   AU.addRequired<LoopInfoWrapperPass>();
   AU.addPreserved<LoopInfoWrapperPass>();
 
-  // We must also preserve LoopSimplify and LCSSA. We locally access their IDs
-  // here because users shouldn't directly get them from this header.
-  extern char &LoopSimplifyID;
-  extern char &LCSSAID;
+  // We must also preserve LoopSimplify and LCSSA.
   AU.addRequiredID(LoopSimplifyID);
   AU.addPreservedID(LoopSimplifyID);
   AU.addRequiredID(LCSSAID);
   AU.addPreservedID(LCSSAID);
 
   // Loop passes are designed to run inside of a loop pass manager which means
   // that any function analyses they require must be required by the first loop
   // pass in the manager (so that it is computed before the loop pass manager