COMP: unset variable in Gcc4.5 path

etc/settings.csh

@@ -121,7 +121,10 @@ case OpenFOAM:
         set gccDir=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH/$gcc_version
         set gmpDir=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH/$gmp_version
         set mpfrDir=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH/$mpfr_version
-        set mpcDir=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH/$mpc_version
+
+        if ( $?mpc_version ) then
+            set mpcDir=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH/$mpc_version
+        endif
 
         # Check that the compiler directory can be found
         if ( ! -d "$gccDir" ) then