overhaul elf csu (c-runtime startup) logic

- more support for linux, android, freebsd, netbsd, openbsd, dragonfly
- centralize musl utils; musl logic is no longer intertwined with csu
- fix musl compilation to build crti/crtn for full archs list
- fix openbsd to support `zig build-lib -dynamic`
- initial dragonfly linking success (with a warning)

ancillary:

- fix emutls (openbsd) tests to use `try`

test/stack_traces.zig

@@ -171,6 +171,7 @@ pub fn addCases(cases: *tests.StackTracesContext) void {
 
     cases.addCase(.{
         .exclude_os = .{
+            .openbsd, // integer overflow
             .windows,
         },
         .name = "dumpCurrentStackTrace",