Disable pch when build on windows for linux (crosscompile)

[slyshykO]

Since none variant of cross-tool knew by me support builds with pch, please, disable it.

[NAThompson]

I don't understand this. There is no obligation to use precompiled headers from our end.

[jzmaddock]

@NAThompson by default the Jamfile that builds the Math TR1 library uses PCH's.

It can be disabled by building with b2 pch=off.

On a practical note, I'm not sure that it's possible for us detect this use case within the Jamfile and adjust pch setting accordingly, and also, does @slyshykO really need to build this library anyway? It's only necessary if you're using the C language interfaces.

[slyshykO]

I have encountered this problem when "build" boost through vcpkg. At this moment, I bypassed the problem by patching Jamfile. I will ask guys from vcpkg how to pass additional parameters to b2.

Do b2 provide information about the host system?