Add support for regex-based target type/pattern specific variables

This is in addition to the already supported path-based target type/pattern
specific variables. For example:

hxx{*}:     x = y  # path-based
hxx{~/.*/}: x = y  # regex-based

1 files changed, 2 insertions, 1 deletions

diff --git a/libbuild2/token.hxx b/libbuild2/token.hxx
index faae466..fca888c 100644
--- a/libbuild2/token.hxx
+++ b/libbuild2/token.hxx
@@ -120,7 +120,8 @@ namespace build2
     // Quoting can be complete, where the token starts and ends with the quote
     // characters and quoting is contiguous or partial where only some part(s)
     // of the token are quoted or quoting continues to the next token. We also
-    // keep track whether the first character of a token is quoted.
+    // keep track whether the first character of a token is quoted (we also
+    // treat escaped first character as quoted).
     //
     quote_type qtype;
     bool qcomp;