[ADT] Fix IWYU for hashing-adjacent files (#194297)

Add explicit includes so these files keep building after we trim
transitive includes from xxhash.h.

For example, FoldingSet.cpp calls llvm::uninitialized_copy, which is
declared in llvm/ADT/STLExtras.h and today reaches the file only
transitively.

Also drop the vestigial `#include "llvm/ADT/Hashing.h"` from
llvm/ADT/STLExtras.h — no name from Hashing.h is used there.

clang-tools-extra/clangd/Config.h

@@ -26,6 +26,7 @@
 
 #include "support/Context.h"
 #include "llvm/ADT/FunctionExtras.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringSet.h"
 #include <functional>

clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h

@@ -14,6 +14,7 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include <optional>
+#include <string>
 
 namespace clang {
 class CXXBaseSpecifier;

llvm/include/llvm/ADT/FoldingSet.h

@@ -16,6 +16,7 @@
 #ifndef LLVM_ADT_FOLDINGSET_H
 #define LLVM_ADT_FOLDINGSET_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/SmallVector.h"

llvm/include/llvm/ADT/STLExtras.h

@@ -18,7 +18,6 @@
 #define LLVM_ADT_STLEXTRAS_H
 
 #include "llvm/ADT/ADL.h"
-#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/iterator.h"

llvm/include/llvm/ADT/StableHashing.h

@@ -18,6 +18,7 @@
 #ifndef LLVM_ADT_STABLEHASHING_H
 #define LLVM_ADT_STABLEHASHING_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/xxhash.h"
 

llvm/include/llvm/ExecutionEngine/Orc/WaitingOnGraph.h

@@ -14,6 +14,7 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/raw_ostream.h"

llvm/lib/Support/FoldingSet.cpp

@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/FoldingSet.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/ErrorHandling.h"

llvm/unittests/Support/xxhashTest.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/xxhash.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;