Improve Linux support

[RaphaelIT7]

While trying to include IVP in my project(https://github.com/RaphaelIT7/gmod-holylib) I encountered a few things which caused issues on Linux or when IVP was combined with the SourceSDK.

What I changed:
[+] Added IVP_NO_PERFORMANCE_TIMER define when the performance timer is not wanted
[+] Added IVP_NO_DEBUGMANAGER define when the debug manager is not wanted
- Also changed IVP_IFDEBUG and added IVP_DEBUGCODE for it's implementation.
[+] Added missing isnan & _finite definitions for Linux into ivp_physics.hxx
[#] Improved Linux support
- added ifdef checks for windows includes & directX functions
[#] Changed IVP_VHash::hash_index
- Fixed the recently added compile error/the two if statements
- Merged both versions of it into a single one
[#] renamed intp to hk_intp (same with uintp)
- Solved compile issues when combined with the sourcesdk where intp was already defined/different.
[#] Changed some asserts to HK_ASSERT
- assert wasn't usable everywhere while HK_ASSERT is.
[#] Fixed a infinite loop on linux
- hk_Memory::memset and hk_Memory::memcpy would call themself recursively until it crashed.
[#] Added get_controller_name to all controllers for debugging.
- previously they would show as sys:unknown which isn't useful at all.
[#] Changed all IVP_IF to IVP_IFDEBUG or IVP_DEBUGCODE if they used the debug manager.
- This solved some crashes when the debug manager was previously disabled.
[-] Removed IVP_Friction_System::sum_energy_destroyed variable since its fully unused.