[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/libraries/j6/include/j6/flags.h

@@ -3,7 +3,8 @@
 /// Enums used as flags for syscalls
 
 enum j6_vm_flags {
-#define VM_FLAG(name, v) j6_vm_flag_ ## name = v,
+    j6_vm_flag_none = 0,
+#define VM_FLAG(name, v) j6_vm_flag_ ## name = (1ul << v),
 #include <j6/tables/vm_flags.inc>
 #undef VM_FLAG
     j6_vm_flag_MAX

src/libraries/j6/include/j6/tables/vm_flags.inc

@@ -1,15 +1,13 @@
-VM_FLAG( none,            0x00000000 )
+VM_FLAG( write,           0 )
+VM_FLAG( exec,            1 )
 
-VM_FLAG( write,           0x00000001 )
-VM_FLAG( exec,            0x00000002 )
+VM_FLAG( contiguous,      4 )
+VM_FLAG( large_pages,     5 )
+VM_FLAG( huge_pages,      6 )
 
-VM_FLAG( contiguous,      0x00000010 )
-VM_FLAG( large_pages,     0x00000020 )
-VM_FLAG( huge_pages,      0x00000040 )
+VM_FLAG( write_combine,   8 )
 
-VM_FLAG( write_combine,   0x00000100 )
+VM_FLAG( mmio,            12 )
 
-VM_FLAG( mmio,            0x00001000 )
-
-VM_FLAG( exact,           0x00010000 )
-VM_FLAG( ring,            0x00020000 )
+VM_FLAG( exact,           16 )
+VM_FLAG( ring,            17 )