build: stop using Make automatic filename expression

[edsiper]

Summary

• preserve the fix and authorship from CMakelists.txt: Stop using Make automatic variable #61 as the first commit
• replace the Make automatic-variable expression with the compiler-provided __FILE__ value
• namespace the definition as __CTR_FILENAME__, matching the library-specific approach used by Cmetrics
• update all internal logging and errno macros to honor __CTR_FILENAME__

Why

CMake 3.20 changed generated Makefile handling in a way that can leave the literal $(subst ... $(abspath $<)) expression embedded in binaries. Besides leaking build paths and failing Yocto build-path QA, the generic __FILENAME__ name can collide with bundled libraries.

The first commit carries the original #61 correction. The second commit gives CTraces its own macro namespace while retaining the existing __FILE__ fallback for ctr_errno().

Validation

• clean CMake development build
• CTest: 4/4 passed
• verified all internal log macros use __CTR_FILENAME__
• verified generated compile commands define __CTR_FILENAME__=__FILE__
• verified the obsolete Make expression is absent from generated compile commands
• git diff --check