Calling @panic made the executable ~30x times bigger, use a simple
`abort()` and let the user figure out what went wrong.
Supporting ARMv6 (and earlier?) platforms is not a priority.
Closes#6676
* Always allocate an info block per-thread so that libc can store
important stuff there.
* Respect ABI-mandated alignment in more places.
* Nicer code, use slices/pointers instead of raw addresses whenever
possible.
This reverts commit ee6fda2297bf75432b8d7115ec4c60c213535bbe, reversing
changes made to f313ab18aecea1ade0b6a90d671352a641ad351a.
This caused a test failure:
```
behavior.misc.test "behavior-arm-linux-none-Debug-bare-multi thread local variable"...test failure
/home/vsts/work/1/s/lib/std/testing.zig:191:14: 0x4608f in std.testing.expect (test)
if (!ok) @panic("test failure");
^
/home/vsts/work/1/s/test/stage1/behavior/misc.zig:616:11: 0x53e93 in behavior.misc.test "behavior-arm-linux-none-Debug-bare-multi thread local variable" (test)
expect(S.t == 1235);
^
```
* Always allocate an info block per-thread so that libc can store
important stuff there.
* Respect ABI-mandated alignment in more places.
* Nicer code, use slices/pointers instead of raw addresses whenever
possible.
