Enabling extra compile warnings

[Rafael Silva]

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 ( #1593 )
• cast-align=strict
• cast-function-type
• cast-qual
• conversion
• dangling-else
• double-promotion ( #1733 )
• duplicated-branches
• float-conversion
• format ( #1592, #1675 )
  • format-overflow=2
  • format-signedness
  • format-truncation
• implicit-fallthrough
• maybe-uninitialized
• missing-attributes
• missing-braces
• char-subscripts ( #1591 )
• null-dereference
• packed
• redundant-decls ( #1733 )
• return-type
• sequence-point
• shadow=local ( #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 ( #1584, #1724 - partial fix )
• pedantic
  • pointer-arith ( #1733 )
  • empty initializers ( #1596 )
  • range expressions ( #1603 )
  • enum forward ref ( #1597 )
  • void with return ( #1598 )
  • binary constants ( #1595 )

[Rachel Mant]

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!