heap.zig: define new default page sizes
heap.zig: add min/max_page_size and their options
lib/std/c: add miscellaneous declarations
heap.zig: add pageSize() and its options
switch to new page sizes, especially in GPA/stdlib
mem.zig: remove page_size
Most of these changes seem like improvements. The PDB thing had a TODO
saying it used to crash; I anticipate it works now, we'll see what CI
does.
The `std.os.uefi` field renames are a notable breaking change.
Implements issue #6451.
This was needed to support allocation on Plan 9 and now other operating
systems like DOS can also use it.
It is a modified version of the WasmAllocator since wasm also uses a
sbrk-esque allocation system.
This commit also adds the necessary system bits for sbrk to work on plan 9.
