Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes.

Differential revision: https://reviews.llvm.org/D23789

llvm-svn: 279535
diff --git a/llvm/lib/Support/FileUtilities.cpp b/llvm/lib/Support/FileUtilities.cpp
index c6a58cc..39dbeff 100644
--- a/llvm/lib/Support/FileUtilities.cpp
+++ b/llvm/lib/Support/FileUtilities.cpp
@@ -14,13 +14,17 @@
 
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cctype>
+#include <cmath>
+#include <cstdint>
 #include <cstdlib>
 #include <cstring>
+#include <memory>
 #include <system_error>
+
 using namespace llvm;
 
 static bool isSignedChar(char C) {
@@ -215,7 +219,7 @@
   }
 
   bool CompareFailed = false;
-  while (1) {
+  while (true) {
     // Scan for the end of file or next difference.
     while (F1P < File1End && F2P < File2End && *F1P == *F2P) {
       ++F1P;