Support TLS Descriptors ABI

[marxin]

The ABI is the default one on AArch64:

• All about thread-local storage
• Fuchsia TLS
• ARM TLSDESC SPEC

One can trigger an unresolved resolution on x86_64 with:

❯ cat tls1.c
#include <stdio.h>

static _Thread_local int x1 = 1;
static _Thread_local int x2;

int main() {
  x2 = 2;

  printf("%d %d\n", x1, x2);
  return 0;
}
$ gcc tls1.c -mtls-dialect=gnu2 -fPIC -B ~/Programming/wild
...
Error: Failed to load symbol `main` (73 local=6) in file #1024 (4/0) (a-tls1.o) (ADDRESS | CAN_BYPASS_GOT) from a-tls1.o (1024 (4/0))

Caused by:
    Unsupported relocation type R_X86_64_GOTPC32_TLSDESC

Steps

• Support x86_64: Initial support for TLS Descriptors (x86_64) #305
• Support AArch64
• Implement relaxations
• Add tests for both C and Rust test-cases