Don't count single quote ' as garbage (#1801)

Also copy the "blank space" (space or tab) vs "whitespace" (space,
tab, or newline) convention from `<ctype.h>`

test/asm/garbage_sequence.asm

@@ -1,3 +1,5 @@
 assert 1 +# 1 == 2
 assert 2 ?<EFBFBD>* 2 == 4
 assert 3 **?<EFBFBD>?##?? 3 == 27
+charmap "x", 4
+assert 4 <<#<EFBFBD>'x' == 64