Unreliable trace method

[lacombar]

The trace method currently used, relying on strance, is unreliable. It fails to handle build system spawning sub-make command. For exemple:

# ls src/
a.cc
# make -C build
Entering .../build/
# clang++ [...] ../src/a.cc

Will fail because clang-tags will fail to intercept the newly spawned instance of make. As a result, its cwd will be ./ instead of ./build and ../src/a.cc will not be considered existent.