systemtap: improve reproducibility

systemtap: improve reproducibility

- Fix build path issue of .pyc files:
  Supply "--root" directory to the "install" command.

- Fix build path issue of c++ object files:
  Use relative dir to include header string_ref.

- Fix build path issue of c library generated by distutils:
  Add OE's CFLAGS which contains `-fdebug-prefix-map' options
  to setup.py

[YOCTO #12528]

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>