[Cmake] CMSYSTEMTOOLS_STANDALONE

[John Biddiscombe]

I wanted to use some of the useful functions present in cmSystemTools in
another project (not CMake), but found I needed to pull in quite a few other
files as well.

I've added
#ifndef CMSYSTEMTOOLS_STANDALONE

#endif // CMSYSTEMTOOLS_STANDALONE

around a number of functions in cmSystemTools.cxx and .h so that I can
define this flag and use the string/directory/other functions without
pulling in cmMakefile etc. The number of places where it was needed was
fairly small, as it tuns out.

The way I've done it I need
cmSystemTools
cmRegularExpression
cmDirectory
in my external project, which seems quite tidy.

I have #ifndef'd out the FindLibrary function because it uses cmMakefile,
and the RunCommand because it pulls in cmWin32ProcessExecution. However, the
run commmand looks quite useful and I wonder if maybe I ought to put it back
in.

Anyway. I feel this is a good thing, but won't commit it if people object.

Comments?

JB