Build directory collision in oryol-test-app when invoking cmake manually.

[floooh]

To reproduce:

Generate out-of-source cmake build files by simply running cmake ../oryol-test-app in a separate build directory (after running 'fips gen' once in oryol-test-app).

The following cmake errors occur, it seems to be related to the module import mechanism used in oryol-test-app (for instance, Oryol itself builds fine this way).

CMake Error at .fips-imports.cmake:122 (add_subdirectory):
  The binary directory

    /Users/floh/projects/build/oryol_Core

  is already used to build a source directory.  It cannot be used to build
  source directory

    /Users/floh/projects/oryol/code/Modules/Core

  Specify a unique binary directory name.
Call Stack (most recent call first):
  CMakeLists.txt:16 (fips_import_oryol_Core)


CMake Error at .fips-imports.cmake:127 (add_subdirectory):
  The binary directory

    /Users/floh/projects/build/oryol_Gfx

  is already used to build a source directory.  It cannot be used to build
  source directory

    /Users/floh/projects/oryol/code/Modules/Gfx

  Specify a unique binary directory name.
Call Stack (most recent call first):
  CMakeLists.txt:17 (fips_import_oryol_Gfx)

Also see https://github.com/floooh/oryol-test-app/issues/1