Avoid some warnings from the generated jamgram.cpp.

Some latest compilers are rather eager intheir warnings. This can cause
problems with the generated grammar code. Hence avoid such warnings when
compiling the grammar parser.

Jamroot.jam

@@ -142,11 +142,18 @@ else
     alias python ;
 }
 
+obj jamgram.obj
+    :   jamgram.cpp
+    :   <toolset>gcc:<cxxflags>-Wno-free-nonheap-object
+    ;
+explicit jamgram.obj ;
+
 local b2_src =
     [ glob src/engine/*.cpp src/engine/modules/*.cpp :
         src/engine/*nt.cpp src/engine/*unix.cpp src/engine/*vms.cpp
         src/engine/yyacc.cpp src/engine/mkjambase.cpp
         src/engine/check_cxx11.cpp
+        src/engine/jamgram.cpp
         ] ;
 local b2_src_nt = [ glob src/engine/*nt.cpp ] ;
 local b2_src_unix = [ glob src/engine/*unix.cpp ] ;
@@ -155,11 +162,11 @@ local unix_os = [ set.difference [ feature.values <target-os> ] : windows vms ]
 
 exe b2
     :   $(b2_src)
+        jamgram.obj
         python
     :   <target-os>windows:<source>$(b2_src_nt)
         <target-os>vms:<source>$(b2_src_vms)
         <target-os>$(unix_os):<source>$(b2_src_unix)
-        <dependency>jamgram.cpp
         <toolset>msvc:<find-static-library>kernel32
         <toolset>msvc:<find-static-library>advapi32
         <toolset>msvc:<find-static-library>user32