Define facilities to control compiler diagnostics and use them for FILENAME

Compiler warnings can be disabled by using the macros defined in
include/rosa/support/diagnostics.h.
The macro FILENAME in include/rosa/config/config.h indexes a C string,
about which some compilers warn (-Wstring-plus-int).
FILENAME is now defined as project_relative_path(FILE)
and the warning is disabled in the function definition.