aarch64: fix compilation warnings

Fix compilation warnings introduced by commit
5b9b7e1d347eb4556084cdccad75e8247c535ed5:

signal.c:702:45: warning: signed and unsigned type in conditional expression [-Wsign-compare]
syscall.c:746:34: warning: initialization from incompatible pointer type [enabled by default]

* syscall.c [AARCH64] (aarch64_sp_ptr): Add explicit cast.
[AARCH64] (arm_sp_ptr): Change pointer type to unsigned.
* linux/aarch64/arch_regs.h (arm_sp_ptr): Update.

Reported-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/linux/aarch64/arch_regs.h b/linux/aarch64/arch_regs.h
index 290a00e..9a5e33e 100644
--- a/linux/aarch64/arch_regs.h
+++ b/linux/aarch64/arch_regs.h
@@ -1,2 +1,2 @@
 extern uint64_t *const aarch64_sp_ptr;
-extern int *const arm_sp_ptr;
+extern uint32_t *const arm_sp_ptr;
diff --git a/syscall.c b/syscall.c
index 59f7d9a..2e536fc 100644
--- a/syscall.c
+++ b/syscall.c
@@ -743,8 +743,8 @@
 } arm_regs_union;
 # define aarch64_regs arm_regs_union.aarch64_r
 # define arm_regs     arm_regs_union.arm_r
-uint64_t *const aarch64_sp_ptr = &aarch64_regs.sp;
-int *const arm_sp_ptr = &arm_regs.ARM_sp;
+uint64_t *const aarch64_sp_ptr = (uint64_t *) &aarch64_regs.sp;
+uint32_t *const arm_sp_ptr = (uint32_t *) &arm_regs.ARM_sp;
 static struct iovec aarch64_io = {
 	.iov_base = &arm_regs_union
 };