[Boost-build] PCH and sources on msvc

From: Vladimir Prus (ghost_at_[hidden])
Date: 2006-10-23 14:27:45

Hi,
I've just committed the attached patch, which makes PCH work on msvc
without requiring a .cpp file -- the .cpp file will be created automatically.

I've checked that command like looks fine, but would appreciate if somebody 
test it with real msvc. For example, try building the example/pch project, or
just remove the .cpp file from sources of cpp-pch target of your project.

(Note: the attached patch has a bug -- ":D" instead of ":D=" -- which was 
fixed by a later commit).

Thanks in advance,
Volodya

        * msvc.jam (msvc-pch-generator.run-pch): Accept
        any number of sources. Don't error out if no .cpp
        file found in sources.
        (compile-c-c++-pch-s): Copied from compile-c-c++-pch.
        (compile-c-c++-pch): Generate temporary .cpp file.
        (compile.c.pch): Forward to compile-c-c++-pch-s or
        compile-c-c++-pch depending on presense of PCH_SOURCE.
        (compile.c++.pch): Likewise.