Fix the following error:

ld: locore.o: non-pic code with imm relocation against dynamic
	symbol `__gp'

With binutils 2.15, ld(1) defines the implicit/automatic symbol __gp
as a dynamic symbol and thus will now complain when used in a non-PIC
fashion (the immediate relocation used to set the GP register). Resolve
this by defining __gp in the linker script. Make sure __gp is aligned
on a 16-byte boundary.

Note: the 0x200000 magic offset is due to having a 22-bit GP-relative
relocation. The GOT will be accessed with negative offsets from GP.

sys/conf/ldscript.ia64

@@ -74,6 +74,8 @@ SECTIONS
     *(.dtors)
     *(SORT(.dtors.*))
   }
+  . = ALIGN(16);
+  __gp = . + 0x200000;
   .got            : { *(.got.plt) *(.got) }
   .IA_64.pltoff   : { *(.IA_64.pltoff) }
   /* We want the small data sections together, so single-instruction offsets