base: add serialized rdtsc function

Use cpuid instruction to prevent the cpu from reordering the rdtsc
instruction when obtaining the TSC value.

Though it is questionable if "mfence; rdtsc" or "rdtscp" would be
a better choice.
base: add Trace API header

This includes the Trace_buffer declaration and definition of most
common functions used to access the buffer and policy.
base: add Trace_session header
core: add Trace_session_component
base: add trace accessors to Thread_base interface
base: add tb_dataspace() to Cpu_session interface
base: add tb_dataspace() to Expanding_c_s_c
core: add TRACE
base: add trace startup-code to _main()
linux: add Expanding_cpu_session_client
linux: add Trace_session_component
linux: initial Trace_session support
foc: add trace_session_component to target.inc
foc: add trace_buffer Cpu_session interface
foc: add trace_buffer start-up to Thread_base
foc: add _session_label to Cpu_session_component
Add trace + trace_session tests
base: add rpc/signal tracepoints header
os: initial Trace_fs server
ports: add noux trace_fs run-script