Add ability to disable use of preprocessed output in compilation

This can be done from a buildfile for a scope (including project root scope)
and per target via cc.reprocess:

cc.reprocess = true
obj{hello}: cc.reprocess = false

As as well externally via config.cc.reprocess:

b config.cc.reprocess=true [configure]

5 files changed, 30 insertions, 16 deletions

diff --git a/build2/c/init.cxx b/build2/c/init.cxx
index 4256e3e..a54060c 100644
--- a/build2/c/init.cxx
+++ b/build2/c/init.cxx
@@ -143,23 +143,24 @@ namespace build2
         v.insert<strings>      ("c.loptions"),
         v.insert<strings>      ("c.libs"),
 
-        v.insert ("cc.poptions"),
-        v.insert ("cc.coptions"),
-        v.insert ("cc.loptions"),
-        v.insert ("cc.libs"),
+        v["cc.poptions"],
+        v["cc.coptions"],
+        v["cc.loptions"],
+        v["cc.libs"],
 
         v.insert<strings>      ("c.export.poptions"),
         v.insert<strings>      ("c.export.coptions"),
         v.insert<strings>      ("c.export.loptions"),
         v.insert<vector<name>> ("c.export.libs"),
 
-        v.insert ("cc.export.poptions"),
-        v.insert ("cc.export.coptions"),
-        v.insert ("cc.export.loptions"),
-        v.insert ("cc.export.libs"),
+        v["cc.export.poptions"],
+        v["cc.export.coptions"],
+        v["cc.export.loptions"],
+        v["cc.export.libs"],
 
-        v.insert ("cc.type"),
-        v.insert ("cc.system"),
+        v["cc.type"],
+        v["cc.system"],
+        v["cc.reprocess"],
 
         v.insert<string>   ("c.std", variable_visibility::project),
 
diff --git a/build2/cc/common.hxx b/build2/cc/common.hxx
index c22140c..3abb086 100644
--- a/build2/cc/common.hxx
+++ b/build2/cc/common.hxx
@@ -63,8 +63,9 @@ namespace build2
       const variable& c_export_loptions;
       const variable& c_export_libs;
 
-      const variable& c_type;   // cc.type
-      const variable& c_system; // cc.system
+      const variable& c_type;       // cc.type
+      const variable& c_system;     // cc.system
+      const variable& c_reprocess;  // cc.reprocess
 
       const variable& x_std;
 
diff --git a/build2/cc/compile.cxx b/build2/cc/compile.cxx
index 32b5f6e..1eb4c9b 100644
--- a/build2/cc/compile.cxx
+++ b/build2/cc/compile.cxx
@@ -567,11 +567,14 @@ namespace build2
         pair<auto_rmfile, bool> p (inject (act, t, lo, src, dd, u));
         dd.close ();
 
-        // If the preprocessed output is suitable for compilation, pass it
-        // along.
+        // If the preprocessed output is suitable for compilation and is not
+        // disabled, pass it along.
         //
-        if (p.second)
-          md.psrc = move (p.first);
+        if (!p.first.path ().empty () && p.second)
+        {
+          if (!cast_false<bool> (t[c_reprocess]))
+            md.psrc = move (p.first);
+        }
 
         md.mt = u ? timestamp_nonexistent : mt;
       }
diff --git a/build2/cc/init.cxx b/build2/cc/init.cxx
index 8d20573..a5fcf83 100644
--- a/build2/cc/init.cxx
+++ b/build2/cc/init.cxx
@@ -78,6 +78,11 @@ namespace build2
       //
       v.insert<bool> ("cc.system");
 
+      // Ability to disable using preprocessed output for compilation.
+      //
+      v.insert<bool> ("config.cc.reprocess", true);
+      v.insert<bool> ("cc.reprocess");
+
       return true;
     }
 
@@ -166,6 +171,9 @@ namespace build2
       rs.assign ("cc.libs") += cast_null<strings> (
         config::optional (rs, "config.cc.libs"));
 
+      if (lookup l = config::omitted (rs, "config.cc.reprocess").first)
+        rs.assign ("cc.reprocess") = *l;
+
       // Load the bin.config module.
       //
       if (!cast_false<bool> (rs["bin.config.loaded"]))
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index 70360bc..395a9f8 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -223,6 +223,7 @@ namespace build2
 
         v["cc.type"],
         v["cc.system"],
+        v["cc.reprocess"],
 
         v.insert<string>   ("cxx.std", variable_visibility::project),