Flat hash map MixingHashState::kSeed broken when build windows shared lib

[Lingfeng-Sun]

Describe the bug

When building windows shared libaray(dll), each dll has their own version of kSeed with different value which cause
static size_t hash(T value) { return static_cast<size_t>(Mix(Seed(), static_cast<uint64_t>(value))); }
return different hash value for the same key for each dll and failed.

Steps to reproduce the bug

Say you have A.dll and B.dll both link to absl, and B.dll dpendent on A.dll
In A.dll you have something like
class SingletonA
{
static SingletonA* Inst()
{
static SingletonA* sInstance = new SingletonA();
}

   SingletonA(){ gTestMap.emplace(100, someObject)};
   absl::flat_hash_map<int, void*> gTestMap;

}

In B.dll you'll get
SingletonA.Inst().gTestMap.find(100) == SingletonA.Inst().gTestMap.end()

What version of Abseil are you using?
latest, 2022.7.25

What operating system and version are you using
windows 10

What compiler and version are you using?

vs2022 with Platform toolset Visual Studio 2019 (v142) c++17 enable

What build system are you using?

cmake 3.23.2

[derekmauro]

We state this in the documentation:

abseil-cpp/absl/hash/hash.h

Lines 43 to 46 in 701185d

	// `absl::Hash` may also produce different values from different dynamically
	// loaded libraries. For this reason, `absl::Hash` values must never cross
	// boundries in dynamically loaded libraries (including when used in types like
	// hash containers.)

We don't have any plans on addressing this.