Issue 2531 fix vs2022 build

[atamagaii]

Okay my plan here is to take a multi stage approach to getting the latest hash_table8 moved into the project.

1. [This PR] Fix all VS2022 build errors including the original shadowing error mentioned in MSVC 2022 17.12.1 configure.py --bootstrap fails on emhash/hash_table8.hpp #2531
2. Target c++14
3. Pull in the latest version of hash_table8

Changes

1. Fixed the variable shadowing in hash_table8. The justification for fixing here instead of taking version 1.7 directly from the emhash project is that we are targeting c++11 and can't support the latest version.
2. We had defined the macro #define unlink _unlink but the compiler still viewed 'unlink' as a POSIX function. I created a function that injects the correct version of unlink depending on the platform.
3. Lots of sign mismatch warnings. Logically something like EXPECT_EQ(list.size(), 1); makes sense, but the compiler doesn't like it. Ideally we would be matching all of our assertions to the exact type. But realistically EXPECT_EQ(list.size(), size_t(1)); and EXPECT_EQ(list.size(), 1u); are going to be equivalent for small values.