Cast to uintptr_t when calling ptrace32 on aix

When I verify my changes to target.h doesn't break build on aix, I get
the following build error on a clean GDB checkout.

../../binutils-gdb/gdb/aix-thread.c: In function 'pdc_read_regs':
../../binutils-gdb/gdb/aix-thread.c:366:4: error: passing argument 3 of 'ptrace32' makes integer from pointer without a cast [-Werror]
    if (!ptrace32 (PTT_READ_GPRS, tid, gprs32, 0, NULL))
    ^
../../binutils-gdb/gdb/aix-thread.c:263:1: note: expected 'long long int' but argument is of type 'uint32_t *'
 ptrace32 (int req, int id, addr_ptr addr, int data, int *buf)
 ^

../../binutils-gdb/gdb/aix-thread.c:375:42: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
       if (!ptrace32 (PTT_READ_FPRS, tid, (addr_ptr) fprs, 0, NULL))
                                          ^

../../binutils-gdb/gdb/aix-thread.c:392:39: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
    if (!ptrace32 (PTT_READ_SPRS, tid, (addr_ptr) &sprs32, 0, NULL))

GCC uses -maix32 in default, so the 'long long' is 64 bit and address
is 32 bit.  Such warnings should go away if -maix64 is used.

In this patch, I cast the parameter to uintptr_t first, and then cast
to addr_ptr.

gdb:

2014-01-07  Yao Qi  <yao@codesourcery.com>
	    Joel Brobecker  <brobecker@adacore.com>

	* aix-thread.c (pdc_read_regs): Cast parameter to uintptr_t.
	(pdc_write_regs): Likewise.
	(fetch_regs_kernel_thread): Likewise.
	(store_regs_kernel_thread): Likewise.