[Self-interest] precompiled header on linux

[Valery Ushakov]

It seems that the makefile fragment to generate the precompiled header
doesn't apply COMPILE_DEFINITIONS (various -D flags) and CXX_FLAGS
(for -O that also affects some internal defines like __NO_INLINE__) at
the time the precompiled header is generated, so all subsequent
compilations generate -Winvalid-pch warnings.  Manually fixing up
$(build)/vm/CMakeFiles/Self.dir/build.make helps, but I don't know any
cmake to fix it properly.  Please, can someone with a cmake clue fix
this?  TIA.

-uwe