std: Slim down the error code path in initStaticTLS

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

lib/std/os/linux/tls.zig

@@ -211,12 +211,16 @@ fn initTLS() void {
         }
     }
 
-    // If the cpu is ARM-based, check if it supports the TLS register
-    if (comptime builtin.arch.isARM() and at_hwcap & std.os.linux.HWCAP_TLS == 0) {
-        // If the CPU does not support TLS via a coprocessor register,
-        // a kernel helper function can be used instead on certain linux kernels.
-        // See linux/arch/arm/include/asm/tls.h and musl/src/thread/arm/__set_thread_area.c.
-        @panic("TODO: Implement ARM fallback TLS functionality");
+    // ARMv6 targets (and earlier) have no support for TLS in hardware
+    // FIXME: Elide the check for targets >= ARMv7 when the target feature API
+    // becomes less verbose (and more usable).
+    if (comptime builtin.arch.isARM()) {
+        if (at_hwcap & std.os.linux.HWCAP_TLS == 0) {
+            // FIXME: Make __aeabi_read_tp call the kernel helper kuser_get_tls
+            // For the time being use a simple abort instead of a @panic call to
+            // keep the binary bloat under control.
+            std.os.abort();
+        }
     }
 
     var tls_align_factor: usize = undefined;