Use CMAKE_CURRENT_SOURCE_DIR instead of CMAKE_SOURCE_DIR

[kmaehashi]

Description

Calculate the path to cudnn-frontend as a relative path from transformer_engine/common/CMakeLists.txt, rather than a relative path from the directory specified to the cmake command.

This will allow other CMake projects to use TransformerEngine as a sub-project (e.g., by adding add_subdirectory(third_party/TransformerEngine/transformer_engine/common) in their CMakeLists.txt) to build TransformerEngine as a part of their build.

Fixes # (issue)

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refractor

Changes

Please list the changes introduced in this PR:

• Use CMAKE_CURRENT_SOURCE_DIR instead of CMAKE_SOURCE_DIR
• Display CUDNN_FRONTEND_INCLUDE_DIR on error

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[timmoon10]

LGTM, thanks for submitting this.