`path_to_fullpath` did different things on Windows&Unix, an attempt to
bring them closer together was made here.
This was prompted by the compiler completely ignoring
`foreign import "foo.dylib"` when `foo.dylib` does not exist (because
`path_to_fullpath` returns an empty string).
Causing just unresolved symbol errors, when on Windows it would pass
along the path to the linker and actually say it doesn't exist, which
is now also the case for Unix.
This also fixes some checker errors that relied on the Windows
behaviour, for example: `Error: File name, , cannot be as a library name
as it is not a valid identifier`.
Made `-no-crt` require either `-default-to-nil-allocator` or
`-default-to-panic-allocator` on Unix, the current default allocators
rely on libc and this was not obvious and would immediately bring up
unresolved symbol errors for the linked memory management functions, or
just link with libc anyways because it was foreign imported.
Added a suggestion to install `nasm` with the user's package manager
when assembling using `nasm` fails on Unix, I saw some confusion about
it in the Discord.
Ignore explicit foreign imports of libc. It is already linked in later
on in the linking process and would otherwise (at least on macOS) cause
linker warnings for duplicate libraries. This also makes it so when
using `-no-crt` and importing something that requires libc, linker
errors are given (like I would expect), instead of silently still
linking with libc because it was foreign imported.
W:\Odin>odin run sketch.odin -file -subsystem:foo
Invalid -subsystem string, got oo. Expected one of:
BOOT_APPLICATION, CONSOLE (default), EFI_APPLICATION, EFI_BOOT_SERVICE_DRIVER, EFI_ROM, EFI_RUNTIME_DRIVER, NATIVE, POSIX, WINDOWS (or WINDOW), WINDOWSCE
We now also set the constant ODIN_WINDOWS_SUBSYSTEM, which is "" for non-Windows targets.
