Jit feature preparation: Introduce "proxy blocks".

When these are invalidated, the block they point to gets invalidated too.

Will be useful to implement various types of block merging and function inlining
without affecting correctness of cache clears etc.

Also, with this commit we can now fully inline replaced functions. fabsf() boils
down to 1-2 instructions and the block continues, for example.
A few more known funcs
Linux build fixes. See #4880
Clean up code pointer naming for the jit.

Now it properly identifies thunk code which is actually a decent percent
when fastmem is off at least.
Increase the min size of an "interesting" func.

Seeing a bunch of forwarders and stuff that won't hash safely.
Replacements: use memmove, avoid invalid addr.

If size = 0, don't care about addresses.  Some games use 0, 0, 0 and
expect it to work just fine, which it should.
Logging tweak.
Merge pull request #4882 from unknownbrackets/jit-minor

Fix memcpy/memmove replacements, minor tweaks
Exclude rt on Mac SDL port
Use GetPointerUnchecked in replaced functions. No point in checking these addresses really.
Call ProxyBlock in ArmJit too. Plus various cleanup and one more string function.
Rework proxy blocks a bit
Reformat JitBlockCache
Blackberry buildfix.
Add direct link to PPSSPP's Twitter page on CreditsScreen.
Use VFS for Flash0 dir on non-Windows/Apple platforms.
Show twitter option for non-Android. (not enabled)
Update native. Fixes #4873
Qt: Remove renaming of 'lowmem' zim so that it can be loaded externally as well. Update version.
A bunch more function hashes