pybindings: Fix a build warning on Fedora

pybindings: Fix a build warning on Fedora

While building python bindings on Fedora 34, gcc 11.3.1 triggers a
build warning:
[1/1] Cythonizing libcgroup.pyx
In file included from /usr/include/bits/libc-header-start.h:33,
                 from /usr/include/limits.h:26,
                 from /usr/lib/gcc/x86_64-redhat-linux/11/include/limits.h:203,
                 from /usr/lib/gcc/x86_64-redhat-linux/11/include/syslimits.h:7,
                 from /usr/lib/gcc/x86_64-redhat-linux/11/include/limits.h:34,
                 from /usr/include/python3.9/Python.h:11,
                 from libcgroup.c:25:
/usr/include/features.h:397:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp]
  397 | #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
      |    ^~~~~~~

the reason being the default compiler flags for c/c++ includes
'-Wp,-D_FORTIFY_SOURCE=2' and '-D_FORTIFY_SOURCE=2'. Whereas Ubuntu
compilers include '-D_FORTIFY_SOURCE=2' option only.  This can be
fixed by adding '-O2' to the CPP Flags in the pybinding Makefile and
there is no side effect in both Fedora and Ubuntu because by default
'-D_FORTIFY_SOURCE=2' is included. The Ubuntu automatically auto
includes '-D_FORTIFY_SOURCE=2' when '-O2' is passed but here it's been
already explicitly passed.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>