align stack properly for calling global ctors/dtors on x86[_64]

failure to do so was causing crashes on x86_64 when ctors used SSE,
which was first observed when ctors called variadic functions due to
the SSE prologue code inserted into every variadic function.

crt/i386/crti.s

 .section .init
 .global _init
 _init:
+	sub $12,%esp
 
 .section .fini
 .global _fini
 _fini:
+	sub $12,%esp

crt/i386/crtn.s

 .section .init
+	add $12,%esp
 	ret
 
 .section .fini
+	add $12,%esp
 	ret

crt/x86_64/crti.s

 .section .init
 .global _init
 _init:
+	push %rax
 
 .section .fini
 .global _fini
 _fini:
+	push %rax

crt/x86_64/crtn.s

 .section .init
+	pop %rax
 	ret
 
 .section .fini
+	pop %rax
 	ret