Adding logic to CMake for -fPIE and -fPIC

[Brad King]

On 5/3/2012 12:02 PM, Stephen Kelly wrote:
> * Make set(CMAKE_POSITION_INDEPENDENT_BINARIES True) set the appropriate flags.

This is the right choice IMO, though the variable should just
initialize a "POSITION_INDEPENDENT" target property.  The target
property would then map to the right flag.  You'll need to factor
out and generalize the CMAKE_SHARED_LIBRARY_${lang}_FLAGS platform
information variable:

  http://cmake.org/gitweb?p=cmake.git;a=blob;f=Modules/Compiler/GNU.cmake;hb=v2.8.8#l24

currently used to add -fPIC to compilation of objects in shared
libraries.  Make its use based on the new property, and simply
make the property true by default for shared libraries.

-Brad