Make gcc's PCH generator ignore the cpp sources, so that

   cpp-pch pch : pch.hpp pch.cpp ;

work both on gcc and msvc.


[SVN r35604]

tools/build

@@ -1 +1 @@
-Subproject commit 806868ce2e41fd4e6e9cf1c82b76aade38d53618
+Subproject commit cbbe68579fee4a2e54a88acf5dd86090a0c2cd4c