[IA64] Allow -mtune=merced for gcc 3.4

Patch submitted by H. J. Lu

  Gcc 3.4.2 fixed ia64 -mtune=merced regressions on Linux 2.6 kernel:

  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16278

  I have been using this patch for several months now.
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/Makefile

@@ -42,8 +42,7 @@ $(error Sorry, your compiler is too old.  GCC v2.96 is known to generate bad cod
 endif
 
 ifeq ($(GCC_VERSION),0304)
-# Workaround Itanium 1 bugs in gcc 3.4.
-#	cflags-$(CONFIG_ITANIUM)	+= -mtune=merced
+	cflags-$(CONFIG_ITANIUM)	+= -mtune=merced
 	cflags-$(CONFIG_MCKINLEY)	+= -mtune=mckinley
 endif