fix the warning introduced by fixing SETTLS clone flag PRE_READ logic

on amd64, vki_modify_ldt_t was defined as void (not very clear why).
sizeof (void) cannot be taken (or more precisely can be taken,
but nobody knows what that means and what gcc does).
So, uncommended the (supposedly) correct definition of the type.
Note that I checked the definition on debian 6.0, kernel 2.6.32
and the structure is still ok.

Still needed to look at the other platforms not properly
handling the *SETTID and the SETTLS flags in clone PRE_READ
logic and/or not defining the type vki_modify_ldt_t



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12589 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/include/vki/vki-amd64-linux.h b/include/vki/vki-amd64-linux.h
index 18e4588..db7b4e0 100644
--- a/include/vki/vki-amd64-linux.h
+++ b/include/vki/vki-amd64-linux.h
@@ -558,11 +558,13 @@
 // type for x86 (the final 'lm' field is added);  I'm not sure about the
 // significance of that... --njn
 
-#if 0
 /* [[Nb: This is the structure passed to the modify_ldt syscall.  Just so as
    to confuse and annoy everyone, this is _not_ the same as an
    VgLdtEntry and has to be translated into such.  The logic for doing
    so, in vg_ldt.c, is copied from the kernel sources.]] */
+/* Note also that a comment in ldt.h indicates that the below
+   contains several fields ignored on 64bit, and that modify_ldt
+   is rather for 32bit. */
 struct vki_user_desc {
 	unsigned int  entry_number;
 	unsigned long base_addr;
@@ -578,9 +580,6 @@
 
 // [[Nb: for our convenience within Valgrind, use a more specific name]]
 typedef struct vki_user_desc vki_modify_ldt_t;
-#endif
-
-typedef void vki_modify_ldt_t;
 
 //----------------------------------------------------------------------
 // From linux-2.6.11.2/include/asm-x86_64/ipcbuf.h