Add %A/%a uppercase/lowercase string format specifiers (#2165)

test/asm/string-formatting.out

@@ -2,5 +2,6 @@
 <4294967254> <-42> <&000037777777726>
 <3.14159> <-00123> <-123.0455932617>
 "\"\\t\" is '\t'     ", "     \"\\t\" is '\t'", "         "\t" is '	'"
-\t\r\0\n
+Hello! HELLO! hello!
+\t\r\0\n \t\r\0\n \t\r\0\n
 -6d:n <300   >