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>`

src/link/lexer.cpp

@@ -260,8 +260,8 @@ yy::parser::symbol_type yylex() {
 	LexerStackEntry &context = lexerStack.back();
 	int c = context.file.sbumpc();
 
-	// First, skip leading whitespace.
-	while (isWhitespace(c)) {
+	// First, skip leading blank space.
+	while (isBlankSpace(c)) {
 		c = context.file.sbumpc();
 	}
 	// Then, skip a comment if applicable.