Add low level OS memory API and arena. Also fixes some compile errors with GCC from recent changes.

[Samdal]

added functionality:

GS_API_DECL void*  gs_memory_reserve(uint32_t size);
GS_API_DECL bool32 gs_memory_commit(void* ptr, uint32_t size);
GS_API_DECL void   gs_memory_decommit(void* ptr, uint32_t size);
GS_API_DECL void   gs_memory_release(void* ptr, uint32_t size);



GS_API_DECL gs_arena*    gs_arena_alloc(void);
GS_API_DECL void         gs_arena_release(gs_arena* arena);

GS_API_DECL void*        _gs_arena_push(gs_arena* arena, uint64_t size_bytes, uint64_t align_bytes);
GS_API_DECL void*        _gs_arena_push_nz(gs_arena* arena, uint64_t size_bytes, uint64_t align_bytes);
GS_API_DECL void         gs_arena_reset(gs_arena* arena);

#define gs_arena_push(a,T) (T*)(_gs_arena_push((a), sizeof(T), _Alignof(T)))
#define gs_arena_push_array(a,T,c) (T*)(_gs_arena_push((a), sizeof(T)*(c), _Alignof(T)))
#define gs_arena_push_no_zero(a,T) (T*)(_gs_arena_push_nz((a), sizeof(T), _Alignof(T)))
#define gs_arena_push_array_no_zero(a,T,c) (T*)(_gs_arena_push_nz((a), sizeof(T)*(c), _Alignof(T)))

GS_API_DECL gs_arena_temp gs_arena_begin_temp(gs_arena* arena);
GS_API_DECL void          gs_arena_end_temp(gs_arena_temp temp);

GS_API_DECL gs_arena_temp gs_arena_get_scratch(gs_arena **conflicts, uint64_t count);
#define gs_arena_release_scratch(scratch) gs_arena_end_temp(scratch)

[Samdal]

closed, see #103