Enabling extra compile warnings

[perigoso]

In the process of working on #1528 the new build-system capabilities were leveraged to enable extra warnings.
This issue lists all desired future extra warnings and tracks whether they pass with the current state of the code-base, along with respective cleanups where needed.

Warnings:

• arith-conversion
• bad-function-cast ( Fix: bad-function-cast warnings #1593 )
• cast-align=strict
• cast-function-type
• cast-qual
• conversion
• dangling-else
• double-promotion ( Feature: declarations cleanup #1733 )
• duplicated-branches
• float-conversion
• format ( Fix: warning format #1592, Wformat (part 2) in gdbserver core and target drivers #1675 )
  • format-overflow=2
  • format-signedness
  • format-truncation
• implicit-fallthrough
• maybe-uninitialized
• missing-attributes
• missing-braces
• char-subscripts ( Fix: char-subscripts warnings #1591 )
• null-dereference
• packed
• redundant-decls ( Feature: declarations cleanup #1733 )
• return-type
• sequence-point
• shadow=local ( Fix: warning shadow #1594 )
• sign-conversion
• stack-protector
• strict-aliasing
• strict-overflow=3
• string-compare
• stringop-overflow
• unknown-pragmas
• unsafe-loop-optimizations
• unsuffixed-float-constants
• unused-const-variable=2
• unused-local-typedefs
• unused
• vla-parameter
• vla ( Fix: ADIv5 DPv0 ID Codes #1584, Feature: Renesas RZ/A1LU support #1724 - partial fix )
• pedantic
  • pointer-arith ( Feature: declarations cleanup #1733 )
  • empty initializers ( Fix: warning pedantic empty init #1596 )
  • range expressions ( Fix: warning pedantic range expr #1603 )
  • enum forward ref ( Fix: enum fwd ref pedantic warning #1597 )
  • void with return ( Fix: warning pedantic void return #1598 )
  • binary constants ( Fix: warning pedantic binary const #1595 )

[dragonmux]

Starting to really get close to this being fixed - chipping away at the warnings little by little as things come into scope to look at. Delighted by what we're seeing!