Debugging notes

* When configuring with --with-asan (likewise with ubsan, etc.), if the linking
  stage fails because of missing ASAN symbols, it will be necessary to to use
  `make LIBS=-lasan`. Though, when using clang in a GNU environment where
  /usr/lib/libasan.so already belongs to gcc, LIBS=-lasan must never be used.

* ASAN may (still) require the use of LD_PRELOAD=/usr/lib/libasan.so.N when it
  complains about having been loaded "too late".

* LSAN's backtraces do not show line information about frames whose code
  resides in dlopened modules. (Prints "(<unknown module>)".) This affects for
  example libkcclient.so. To work around this, let ld.so preload the module by
  using LD_PRELOAD=libkcclient.so. The future dlopen call will return the
  *same* handle when it opens the same file, thanks to a common optimization in
  libdl.so.
