boost: fixed to actually define the right "toolset"

develop/boost/boost.conf

@@ -20,9 +20,12 @@ makeinstopt=
 # otherwise rebuilding boost does not reinstall static files
 var_insert taropt ' ' -m
 
-hook_add inmake 5 "bjam -j $SDECFG_PARALLEL_MAX -sTOOLS=$CC"
-hook_add postmake 5 "bjam --prefix=$prefix --libdir=$libdir \
-                     --includedir=$includedir -sTOOLS=$CC --layout=system \
-                     install"
+bjamopt=
+var_append bjamopt ' ' "toolset=$CC"
 
+hook_add inmake 5 "bjam -j $SDECFG_PARALLEL_MAX $bjamopt"
+hook_add postmake 5 "bjam $bjamopt --prefix=$prefix --libdir=$libdir \
+                     --includedir=$includedir --layout=system \
+                     install"
 
+unset bjamopt