Gold: Fix mips.cc for GCC 4.2

GCC 4.2 fails to compile "(uint64_t) 0x800080008000" with

error: integer constant is too large for ‘long’ type

This patch adds "llu" suffix to 0x800080008000 for GCC 4.2.

	* mips.cc (Mips_relocate_functions): Add "llu" suffix to
	0x800080008000.