Implement support for excluded and ad hoc prerequisites

The inclusion/exclusion is controlled via the 'include' prerequisite-specific
variable. Valid values are:

false  - exclude
true   - include
adhoc  - include but treat as an ad hoc input

For example:

lib{foo}: cxx{win32-utility}: include = ($cxx.targe.class == 'windows')
exe{bar}: libs{plugin}: include = adhoc

1 files changed, 3 insertions, 0 deletions

diff --git a/build2/version/rule.cxx b/build2/version/rule.cxx
index 1a41cef..91b8c75 100644
--- a/build2/version/rule.cxx
+++ b/build2/version/rule.cxx
@@ -60,6 +60,9 @@ namespace build2
       bool fi (false); // Found in.
       for (prerequisite_member p: group_prerequisite_members (a, t))
       {
+        if (include (a, t, p) != include_type::normal) // Excluded/ad hoc.
+          continue;
+
         fm = fm || manifest_prerequisite (rs, p);
         fi = fi || p.is_a<in> ();
       }