[libc] Fix random SSE alignment GP faults

The libc CRT _start function had a stray pop left in it, which was
causing the stack to never be 16-byte aligned and thus causing crashes
when SSE instructions were called.

src/libraries/libc/arch/amd64/crt/crt0.s

@@ -17,7 +17,7 @@ _libc_crt0_start:
 
     call __init_libc
 
-    pop rdi
+    mov rdi, 0
     mov rsi, rsp
     mov rdx, 0    ; TODO: actually parse stack for argc, argv, envp
     mov rcx, rbx