Add support for default extension specification, trailing dot escaping

For example:

cxx{*}: extension = cxx

cxx{foo}         # foo.cxx
cxx{foo.test}    # foo.test      (probably what we want...)
cxx{foo.test...} # foo.test.cxx  (... is this)
cxx{foo..}       # foo.
cxx{foo....}     # foo..
cxx{foo.....}    # error (must come in escape pair)

1 files changed, 5 insertions, 1 deletions

diff --git a/build2/in/target.cxx b/build2/in/target.cxx
index fec1135..4bc9d6a 100644
--- a/build2/in/target.cxx
+++ b/build2/in/target.cxx
@@ -34,7 +34,11 @@ namespace build2
     }
 
     static bool
-    in_pattern (const target_type&, const scope&, string&, bool)
+    in_pattern (const target_type&,
+                const scope&,
+                string&,
+                optional<string>&,
+                bool)
     {
       fail << "pattern in in{} prerequisite" << endf;
     }