nptl:arm: add a wrapper for .cfi_sections pseudo-ops

nptl:arm: add a wrapper for .cfi_sections pseudo-ops

ARM disables by default the support for ASM CFI directives.
Anyway using an old version of binutils that does not support some new
pseudo-op, the build fails as below:

  AS libpthread/nptl/sysdeps/unix/sysv/linux/close.oS
libpthread/nptl/sysdeps/unix/sysv/linux/close.S: Assembler messages:
libpthread/nptl/sysdeps/unix/sysv/linux/close.S:9: Error: unknown pseudo-op: `.cfi_sections'

The problem is that the .cfi_sections pseudo should be wrapped by a macro
that expands to nothing when the CFI is off.

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>
CC: Khem Ray <ray.khem@gmail.com>