[util] Remove enum_bitfields

The enum_bitfields system never worked quite right, and always had edge cases where name
resolution for the SFINAE would fail. Move everything over to use util::bitset, which can
be constexpr and boils down to inline integer bitops in release mode.

Improved util::bitset itself, moving the array-backed base implementation into a new
util::sized_bitset, and making the single-inttype backed implementation the base case.
Also added a distinction between | or |= (which work with real bit values) and + or +=
(which work with bit indexes).

src/user/ld.so/image.cpp

@@ -94,7 +94,7 @@ load_image(image_list::item_type &img, j6::proto::vfs::client &vfs)
         // TODO: way to remap VMA as read-only if there's no write flag on
         // the segment
         unsigned long flags = j6_vm_flag_exact | j6_vm_flag_write;
-        if (seg.flags && elf::segment_flags::exec)
+        if (seg.flags.get(elf::segment_flags::exec))
             flags |= j6_vm_flag_exec;
 
         uintptr_t start = file.base() + seg.offset;

src/user/srv.init/j6romfs.h

@@ -3,7 +3,6 @@
 /// Data structure for dealing with j6romfs images
 
 #include <util/counted.h>
-#include <util/enum_bitfields.h>
 
 namespace j6romfs
 {

src/user/srv.init/loader.cpp

@@ -95,7 +95,7 @@ load_program_into(j6_handle_t proc, elf::file &file, uintptr_t image_base, const
         // TODO: way to remap VMA as read-only if there's no write flag on
         // the segment
         unsigned long flags = j6_vm_flag_write;
-        if (seg.flags && elf::segment_flags::exec)
+        if (seg.flags.get(elf::segment_flags::exec))
             flags |= j6_vm_flag_exec;
 
         uintptr_t start = file.base() + seg.offset;