Renamed TRACY_NO_SYS_TRACE -> TRACY_NO_SYSTEM_TRACING to match the
build flag name. Unlike the meson logic, the CMake logic directly
maps the option name to the build flag that is injected. With the
mismatched name, the flag wasn't being properly applied.
Added TRACY_TIMER_FALLBACK option to expose the same-named flag.
Moved signal.h include to get sigaction definition that was missing when
TRACY_NO_CALLSTACK was defined.
This usually prevents the compiler from emitting warnings about stuff it found in
the included files.
Since the CMakeLists.txt seems to be exclusively meant for code that is making use
of Tracy rather than Tracy itself using it to build, silencing the warnings should probably
be what most folks would want.
This will prevent things like #126
