Android-specific: check for execinfo.h and disable backtrace if not detected.
Revert "Split fx_vasprintf() to fx_vasprintf() and fx_strdup(): not all implementations allow integer NULL in args."

This reverts commit 673458f6e0c1e85308102bc17bfe3635937a96c8.
Fix production mode support in CMakeLists.txt.

It is wrong to check ${CMAKE_PROJECT_NAME} for emptiness because on
CMake re-runs it always contains a non-empty value. Compensate for it by
checking the variable only on first run and caching the result.
Add a va_list wrapper for fx_vasprintf() to be able to accept explicitly null args.

On some architectures (notably, Android/ARM) va_list is not a pointer.
Android-specific: do not build long double parsers.
Add an arbitrary base logarithm function and use it instead of C99-only log2().
Use ${CMAKE_DL_LIBS} instead of searching for "dl".
Android-specific: do not build POSIX plugin engine.

RTLD_NOLOAD is not available.
Android-specific: also do not build POSIX timer backend.

clock_nanosleep(), at least, is not available.
Android-specific: Do not use -fuse-linker-plugin (unsupported by the toolchain).
Teardown the logger.

It became unmaintainable and VERY non-standard-compliant.
Rewrite is underway.
Fix Common.cmake: use CURRENT_SOURCE_DIR in add_fixed_library_group.
Add a define whose value equals to sizeof(void*).
Add recursive dep handling in production mode.

This adds a new file to CMake inter-project API:
"CMakeConfigureProduction.cmake".

It shall contain calls to
- add_production_build_library (...)
- add_production_build_library_custom (...)
- list (APPEND LIBRARIES ...)

Its purpose is to recursively gather base include pathes for all
sub-projects and add them to the top-level project.

It is needed as API headers for sub-projects often reference
API headers of their own sub-projects.
Cut semicolon after (Declare|Implement)Descriptor - thus silence the -pedantic.
Fix CHECKVALUE handling in assertion and separate it from the API.
Reformat Common.cmake
Improve timeops measure reporting.
Remove some clang-unsupported warnings from common set.
Add pthreads to static include files.