Remove unused / ambiguously used defines

We sometimes use LINUXSPARC and sometimes (more often)
use "defined(SPARC) || defined(SPARC64)". Better to use
one construct consistently.
LINUX_MIPS64 is altogether unused.

* defs.h: Remove LINUXSPARC and LINUX_MIPS64 defines.
Move PTRACE_xxx compat defines up, before arch-specific
machinery. Use defined(SPARC) || defined(SPARC64)
instead of LINUXSPARC.
* file.c: Use defined(SPARC) || defined(SPARC64) instead of LINUXSPARC.
* signal.c: Likewise.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/signal.c b/signal.c
index 5a4a8d5..5e862ad 100644
--- a/signal.c
+++ b/signal.c
@@ -1261,7 +1261,7 @@
 	 * therefore tcp->u_arg[3(4)] _must_ be NSIG / 8 here,
 	 * and we always use smaller memcpy. */
 	sigemptyset(&sigset);
-#ifdef LINUXSPARC
+#if defined(SPARC) || defined(SPARC64)
 	if (tcp->u_arg[4] <= sizeof(sigset))
 		memcpy(&sigset, &sa.sa_mask, tcp->u_arg[4]);
 #else
@@ -1283,7 +1283,7 @@
 	if (entering(tcp))
 		tprints(", ");
 	else
-#ifdef LINUXSPARC
+#if defined(SPARC) || defined(SPARC64)
 		tprintf(", %#lx, %lu", tcp->u_arg[3], tcp->u_arg[4]);
 #elif defined(ALPHA)
 		tprintf(", %lu, %#lx", tcp->u_arg[3], tcp->u_arg[4]);