[srv.init] Create init server and read init args

Create a new usermode program, srv.init, and have it read the initial
module_page args sent to it by the bootloader. Doesn't yet do anything
useful but sets up the way for loading the rest of the programs from
srv.init.

Other (mostly) related changes:

- bootloader: The allocator now has a function for allocating init
  modules out of a modules_page slab. Also changed how the allocator is
  initialized and passes the allocation register and modules_page list
  to efi_main().
- bootloader: Expose the simple wstrlen() to the rest of the program
- bootloader: Move check_cpu_supported() to hardware.cpp
- bootloader: Moved program_desc to loader.h and made the loader
  functions take it as an argument instead of paths.
- kernel: Rename the system_map_mmio syscall to system_map_phys, and
  stop having it default those VMAs to having the vm_flags::mmio flag.
  Added a new flag mask, vm_flags::driver_mask, so that drivers can be
  allowed to ask for the MMIO flag.
- kernel: Rename load_simple_process() to load_init_server() and got rid
  of all the stack setup routines in memory_bootstrap.cpp and task.s
- Fixed formatting in config/debug.toml, undefined __linux and other
  linux-specific defines, and got rid of _LIBCPP_HAS_THREAD_API_EXTERNAL
  because that's just not true.

src/boot/loader.h

@@ -7,6 +7,7 @@
 namespace kernel {
 namespace init {
 	struct program;
+	struct module;
 }}
 
 namespace boot {
@@ -17,25 +18,37 @@ namespace fs {
 
 namespace loader {
 
+struct program_desc
+{
+	const wchar_t *name;
+	const wchar_t *path;
+};
+
 /// Load a file from disk into memory.
 /// \arg disk  The opened UEFI filesystem to load from
-/// \arg name  Name of the module (informational only)
-/// \arg path  Path on `disk` of the file to load
+/// \arg desc  The program descriptor identifying the file
 buffer
 load_file(
 	fs::file &disk,
-	const wchar_t *name,
-	const wchar_t *path);
+	const program_desc &desc);
 
 /// Parse and load an ELF file in memory into a loaded image.
-/// \arg program  The program structure to fill
-/// \arg name     The name of the program being loaded
-/// \arg data     Buffer of the ELF file in memory
-void
+/// \arg disk       The opened UEFI filesystem to load from
+/// \arg desc       The program descriptor identifying the program
+/// \arg add_module Also create a module for this loaded program
+kernel::init::program *
 load_program(
-	kernel::init::program &program,
-	const wchar_t *name,
-	buffer data);
+	fs::file &disk,
+	const program_desc &desc,
+	bool add_module = false);
+
+/// Load a file from disk into memory, creating an init args module
+/// \arg disk  The opened UEFI filesystem to load from
+/// \arg desc  The program descriptor identifying the file
+void
+load_module(
+	fs::file &disk,
+	const program_desc &desc);
 
 /// Verify that a loaded ELF has the j6 kernel header
 /// \arg program  The program to check for a header