Use the compiler builtin for the ARM thread id.

The mrc to c13/c0/3 (thread id register) is undefined on ARMv5 (e.g.
ARM926EJ-S) and SIGILL'd during init. __builtin_thread_pointer lowers
to the same mrc on targets with a thread pointer register and to
__aeabi_read_tp on soft-TLS targets.

public/client/tracy_rpmalloc.cpp

@@ -743,7 +743,7 @@ get_thread_id(void) {
 	__asm__("movq %%fs:0, %0" : "=r" (tid) : : );
 #    endif
 #  elif defined(__arm__)
-	__asm__ volatile ("mrc p15, 0, %0, c13, c0, 3" : "=r" (tid));
+	tid = (uintptr_t)__builtin_thread_pointer();
 #  elif defined(__aarch64__)
 #    if defined(__MACH__)
 	// tpidr_el0 likely unused, always return 0 on iOS