Make is___kvaddrspace_vaddr() portable

[latentPrion]

zambesii/m4/cxxrtl-ctors.m4

Lines 21 to 24 in 67ea81f

	is___kvaddrspace_vaddr() {
	local hex_word="$1"
	test -n "$hex_word" && test "$(printf "%d" "0x${hex_word:0:1}")" -ge 8
	}

Function is___kvaddrspace_vaddr() is arch-specific, but not guarded by sufficient per-arch guards fir portability.