Add POPCOUNT function (#2166)

test/asm/bit-functions.asm

@@ -9,3 +9,9 @@ assert TZCOUNT(-1) == 0
 assert TZCOUNT($80000000) == 31
 
 assert TZCOUNT(1.0) == 16
+
+assert POPCOUNT(0) == 0
+assert POPCOUNT(1) == 1
+assert POPCOUNT(-1) == 32
+assert POPCOUNT(%10101100) == 4
+assert POPCOUNT(-%10101100) == 27