Add missing header for uint64_t

[pmatos]

Summary

LLVM fails to build in some environments with EXPENSIVE_CHECKS
due to the use of uint64_t without including cstdint.

[pmatos]

Adding Jay and Nikita as reviewers since they authored and approved the related revision D120123 .
I have noticed that in some environment with EXPENSIVE_CHECKS, LLVM fails to build due to undefined uint64_t used in line 234.

[nikic]

LG

llvm/include/llvm/Pass.h

 // bottom), so the APIs exposed by these files are also automatically available
 // to all users of this file.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_PASS_H
 #define LLVM_PASS_H
 
+#ifdef EXPENSIVE_CHECKS
+#include <cstdint>
+#endif
 #include <string>
 
 namespace llvm {
 
 class AnalysisResolver;
 class AnalysisUsage;
 class Function;
 class ImmutablePass;