Fix brace matching in the presence of digit separators, closes #862

If the `'` is preceded by a digit then it is a digit separator, not the start of a character literal

Author: hsutter

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.3.0   Build 8C13:1356
+cppfront compiler v0.3.0   Build 8C13:1859
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"8C13:1356"
+"8C13:1859"

source/io.h

@@ -782,7 +782,10 @@ auto process_cpp2_line(
                 if (prev != '\\' || prev2 == '\\') { in_string_literal = true; }
 
             break;case '\'':
-                if (prev != '\\' || prev2 == '\\') { in_char_literal = true; }
+                if (prev != '\\' || prev2 == '\\') {
+                    //  Also check that this isn't a digit separator
+                    in_char_literal = !is_hexadecimal_digit(prev);
+                }
 
             break;default: ;
             }