Allow packages to use project()

[masterleinad]

trilinos/Trilinos#11779 explores using Kokkos as a native CMake project within Trilinos' TriBITS build system. In the process, I noticed that tribits_package_postprocess doesn't work properly if the package uses project(), see https://github.com/trilinos/Trilinos/pull/11779/files#r1196855222, since

TriBITS/tribits/core/package_arch/TribitsPackageMacros.cmake

Line 870 in b669da7

if (${PACKAGE_NAME}_SOURCE_DIR STREQUAL ${PROJECT_NAME}_SOURCE_DIR)

would report that the code is executed at the top level instead of at the package level and then set ${PACKAGE_NAME}_TRIBITS_PACKAGE_POSTPROCESS in the same scope instead of in the parent scope.
Using $(CMAKE_PROJECT_NAME}_SOURCE_DIR) instead of $(PROJECT_NAME}_SOURCE_DIR) fixes this for me.
Note that there might be more cases where it would be more appropriate to check for CMAKE_PROJECT_NAME instead of PROJECT_NAME but this appears sufficient for my case.

[bartlettroscoe]

I will take care of this when I extend the TriBITS example/test case TribitsExampleProject2/packages/packages1/ to use a raw CMake build system to be TriBITS-compliant for an internal build with calling no TriBITS code.