Add missing file

[SVN r83790]

src/build/config-cache.jam

@@ -0,0 +1,63 @@
+# Copyright 2012 Steven Watanabe
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
+
+import modules ;
+import errors ;
+import regex ;
+import path ;
+import project ;
+
+rule get ( name )
+{
+    return $(.vars.$(name)) ;
+}
+
+rule set ( name : value * )
+{
+    .all-vars += $(name) ;
+    .vars.$(name) = $(value) ;
+}
+
+rule save ( )
+{
+    if $(.cache-file)
+    {
+        local target = <new-cache-file>$(.cache-file) ;
+        local contents = "# Automatically generated by Boost.Build.\n# Do not edit.\n\nmodule config-cache {\n" ;
+        for local var in $(.all-vars)
+        {
+            local transformed ;
+            for local value in $(.vars.$(var))
+            {
+                transformed += [ regex.escape $(value) : \"\\ : \\ ] ;
+            }
+            local quoted = \"$(transformed)\" ;
+            contents += "  set \"$(var)\" : $(quoted:J= ) ;\n" ;
+        }
+        contents += "}\n" ;
+        FILE_CONTENTS on $(target) = $(contents) ;
+        ALWAYS $(target) ;
+        config-cache.write $(target) ;
+        UPDATE_NOW $(target) : [ modules.peek configure : .log-fd ] : ignore-minus-n ;
+    }
+}
+
+actions write
+{
+    @($(STDOUT):E=$(FILE_CONTENTS:J=)) > "$(<)"
+}
+
+rule load ( cache-file )
+{
+    if $(.cache-file)
+    {
+        errors.error duplicate load of cache file ;
+    }
+    cache-file = $(cache-file) ;
+    if [ path.exists $(cache-file) ] && ! ( --reconfigure in [ modules.peek : ARGV ] )
+    {
+        include <old-cache-file>$(cache-file) ;
+    }
+    .cache-file = $(cache-file) ;
+}