Rename procutils_read_file to __libc_procutils_read_file [BZ #31755]

Fix BZ #31755 by renaming the internal function procutils_read_file to
__libc_procutils_read_file.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>