[CMake] Updated FindThreads.cmake in tracker

[Hendrik Sattler]

Zitat von Philip Lowman <philip at yhbt.com>:
> So the gist of it is, if your only Unix compiler is gcc and if you add
> "-pthread" to your CMAKE_C_FLAGS/CMAKE_CXX_FLAGS you really have no need for
> FindThreads at all, as far as I can tell.

But cmake is not only about gcc. Additionally, gcc > 3.0 is mentioned,  
gcc-2.95 may still be in use somewhere.
So, testing for -pthread if gcc > 3.0 is used should be the first  
action in FindThreads.cmake. OTOH, this is so compiler and platform  
specific, it should go with the normal compiler and platform files.  
There, it could be a simple define instead of testing -> much faster.

HS