thread support broken on ppc-aix.

thread support broken on ppc-aix.

Thread support got broken when adding 64bit support on ppc-aix.
Upon digging further, I found that the following patch...

   | * gdb_ptrace.h: Use ptrace64 instead of ptrace if HAVE_PTRACE64
   | is defined.
   | * rs6000-nat.c: Check for __ld_info64_ if compiling 64 BIT gdb.
   | (rs6000_ptrace32): Call ptrace64 instead of ptrace if present.
   | (rs6000_ptrace64): Call ptace64 instead of ptracex if present.
   | * configure.ac: Check for ptrace64.
   | * configure, config.in: Regenerate.

... is responsible for this regression:

    (gdb) x /x &__n_pthreads
    0xf06a8258 <__n_pthreads>: Cannot access memory at address 0xf06a8258

Prior to the patch, we have:

    (gdb) x /x &__n_pthreads
    0xf06a8258 <__n_pthreads>: 0x00000003

The problem occurs inside rs6000_ptrace32, while calling ptrace64.
The address is given to rs6000_ptrace32 as an "int *", while
ptrace64 takes a "long long". The cast causes the address to be
sign-extended, which results in GDB trying to read the wrong address.

This patch fixes the issue by casting the address to a "uintptr_t"
instead, and letting the compiler do the implicit conversion to
"long long" in the function call.

gdb/ChangeLog:

        * rs6000-nat.c (rs6000_ptrace32): Cast "addr" to "uintptr_t"
        instead of "long long" in call to ptrace64.