Redesign obj to exe/lib mapping

Specifically:

* objso{} and libso{} target types have been renamed to objs{} and libs{}

* obje{} has been added (so now we have obje{}, obja{}, and objs{})

* obje{} is now used for building exe{}

* object file extensions have been changed to use "hierarchical extensions"
  that reflect the extension of the corresponding exe/lib target (instead of
  the -so suffix we used), specifically:

  obje{}: foo.o, (UNIX), foo.exe.o (MinGW), foo.exe.obj (Windows)
  obja{}: foo.a.o (UNIX, MinGW), foo.lib.obj (Windows)
  objs{}: foo.so.o (UNIX), foo.dylib.o (Darwin), foo.dll.o (MinGW),
          foo.dll.obj (Windows)

1 files changed, 70 insertions, 0 deletions

diff --git a/build2/cxx/common.cxx b/build2/cxx/common.cxx
new file mode 100644
index 0000000..0b66eb5
--- /dev/null
+++ b/build2/cxx/common.cxx
@@ -0,0 +1,70 @@
+// file      : build2/cxx/common.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <build2/cxx/common>
+
+#include <build2/variable>
+#include <build2/algorithm>
+
+using namespace std;
+
+namespace build2
+{
+  namespace cxx
+  {
+    using namespace bin;
+
+    lorder
+    link_order (scope& bs, otype ot)
+    {
+      const char* var;
+
+      switch (ot)
+      {
+      case otype::e: var = "bin.exe.lib";  break;
+      case otype::a: var = "bin.liba.lib"; break;
+      case otype::s: var = "bin.libs.lib"; break;
+      }
+
+      const auto& v (cast<strings> (bs[var]));
+      return v[0] == "shared"
+        ? v.size () > 1 && v[1] == "static" ? lorder::s_a : lorder::s
+        : v.size () > 1 && v[1] == "shared" ? lorder::a_s : lorder::a;
+    }
+
+    target&
+    link_member (bin::lib& l, lorder lo)
+    {
+      bool ls (true);
+      const string& at (cast<string> (l["bin.lib"])); // Available members.
+
+      switch (lo)
+      {
+      case lorder::a:
+      case lorder::a_s:
+        ls = false; // Fall through.
+      case lorder::s:
+      case lorder::s_a:
+        {
+          if (ls ? at == "static" : at == "shared")
+          {
+            if (lo == lorder::a_s || lo == lorder::s_a)
+              ls = !ls;
+            else
+              fail << (ls ? "shared" : "static") << " variant of " << l
+                   << " is not available";
+          }
+        }
+      }
+
+      target* r (ls ? static_cast<target*> (l.s) : l.a);
+
+      if (r == nullptr)
+        r = &search (ls ? libs::static_type : liba::static_type,
+                     prerequisite_key {nullptr, l.key (), nullptr});
+
+      return *r;
+    }
+  }
+}