Building newlib with clock_gettime()

Hi!

I'm trying to build a RISC-V GNU compiler with *clock_gettime()* provided
by newlib. It seems that building the toolchain by default does *not* enable
this function -- looking at the libstdc++ library config settings shows
that any symbols regarding *clock_gettime()* are disabled*.*

I'm wondering if there's anything specific that can be done to have this
function provided by newlib.
Here's the command that newlib was built with:

$  /nobackup/build/riscv-gnu-toolchain/newlib/configure
--target=riscv64-unknown-elf --prefix=/nobackup/build/riscv64-unknown-elf
--enable-newlib-io-long-double --enable-newlib-io-long-long
--enable-newlib-io-c99-formats
--enable-newlib-reigster-fini CFLAGS_FOR_TARGET=-O2 -D_POSIX_MODE
-ffunction-sections -fdata-sections    -mcmodel=medlow
CXXFLAGS_FOR_TARGET=-O2 -D_POSIX_MODE -ffunction-sections -fdata-sections
  -mcmodel=medlow

Thanks!