std.debug.SelfInfo: remove shared logic

There were only a few dozen lines of common logic, and they frankly
introduced more complexity than they eliminated. Instead, let's accept
that the implementations of `SelfInfo` are all pretty different and want
to track different state. This probably fixes some synchronization and
memory bugs by simplifying a bunch of stuff. It also improves the DWARF
unwind cache, making it around twice as fast in a debug build with the
self-hosted x86_64 backend, because we no longer have to redundantly go
through the hashmap lookup logic to find the module. Unwinding on
Windows will also see a slight performance boost from this change,
because `RtlVirtualUnwind` does not need to know the module whatsoever,
so the old `SelfInfo` implementation was doing redundant work. Lastly,
this makes it even easier to implement `SelfInfo` on freestanding
targets; there is no longer a need to emulate a real module system,
since the user controls the whole implementation!

There are various other small refactors here in the `SelfInfo`
implementations as well as in the DWARF unwinding logic. This change
turned out to make a lot of stuff simpler!

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/std/debug/Dwarf.zig b/lib/std/debug/Dwarf.zig
index cfba366162..7af76d02a1 100644
--- a/lib/std/debug/Dwarf.zig
+++ b/lib/std/debug/Dwarf.zig
@@ -28,6 +28,7 @@ const Dwarf = @This();
 
 pub const expression = @import("Dwarf/expression.zig");
 pub const Unwind = @import("Dwarf/Unwind.zig");
+pub const SelfUnwinder = @import("Dwarf/SelfUnwinder.zig");
 
 /// Useful to temporarily enable while working on this file.
 const debug_debug_mode = false;
@@ -1458,8 +1459,8 @@ pub fn spRegNum(arch: std.Target.Cpu.Arch) u16 {
 
 /// Tells whether unwinding for this target is supported by the Dwarf standard.
 ///
-/// See also `std.debug.SelfInfo.supports_unwinding` which tells whether the Zig
-/// standard library has a working implementation of unwinding for this target.
+/// See also `std.debug.SelfInfo.can_unwind` which tells whether the Zig standard
+/// library has a working implementation of unwinding for the current target.
 pub fn supportsUnwinding(target: *const std.Target) bool {
     return switch (target.cpu.arch) {
         .amdgcn,