compilefix gcc 11

based on compile fix from upstream
https://www.gitmemory.com/issue/maekitalo/cxxtools/30/770247974

Signed-off-by: Joerg Bornkessel <hd_brummy@gentoo.org> (09 May 2021)
diff -Naur cxxtools-3.0.orig/include/cxxtools/char.h cxxtools-3.0/include/cxxtools/char.h
--- cxxtools-3.0.orig/include/cxxtools/char.h	2021-05-09 18:32:41.415653108 +0200
+++ cxxtools-3.0/include/cxxtools/char.h	2021-05-09 18:33:56.117653108 +0200
@@ -68,9 +68,10 @@
             typedef int32_t value_type;
 
             //! Constructs a character with a value of 0.
-            Char()
-            : _value(0)
-            {}
+//            Char()
+//            : _value(0)
+//            {}
+            Char() = default;
 
             //! Constructs a character using the given value as base for the character value.
             Char(value_type ch)