Don't include <asm/ia64regs.h> unnecessarily.

We only need that header when compiling with icc, since the gcc variant of
ia64_get_bsp() uses in-line assembly code.  Per report from Frank Brendel,
the header doesn't exist on all IA64 platforms; so don't include it unless
we need it.

src/backend/tcop/postgres.c

@@ -2697,7 +2697,9 @@ ProcessInterrupts(void)
  */
 #if defined(__ia64__) || defined(__ia64)
 
+#ifdef __INTEL_COMPILER
 #include <asm/ia64regs.h>
+#endif
 
 static __inline__ char *
 ia64_get_bsp(void)