TF2: Fix tier1 not compiling with /std:c++20 on msvc

[EricZhang456]

MSVC wouldn't compile public/tier1/UtlSortVector.h with C++20

C:\Users\Eric Zhang\Documents\stuff\hl2sdk\public\tier1\UtlSortVector.h(247): error C3861: 'Base': identifier not found
C:\Users\Eric Zhang\Documents\stuff\hl2sdk\public\tier1\UtlSortVector.h(247): note: 'Base': function declaration must be available as none of the arguments depend on a template parameter
C:\Users\Eric Zhang\Documents\stuff\hl2sdk\public\tier1\UtlSortVector.h(247): error C3861: 'Count': identifier not found
C:\Users\Eric Zhang\Documents\stuff\hl2sdk\public\tier1\UtlSortVector.h(247): note: 'Count': function declaration must be available as none of the arguments depend on a template parameter

Not sure why this is the case, but the fix is simple enough. Might be the same case for other branches as well.

[Kenzzer]

This seems... odd ? I'm not doubting the fix here, but the compiler error seems wrong. I'm going to hold off merging this until I can investigate on my side.