This fixes a compile error on gnu compilers where __tls_guard could be defined twice.

Cianciosa, Markrequested to merge
fix_tls_guard_errors into main

This change fixes an issue on GNU compilers where the intrinsic __tls_guard could be defined twice depending on how headers were included. Additionally this removes some unnecessary namespace qualifiers and adds a missing header file in precompiled headers list.

__tls_guard fix by @o3e.

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