package/uclibc: enable Linuxthreads for riscv64
Since commit:
https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/commit/?id=1640c262dc63e2f8f43c0728dbe867c8fffe3e9d
Linuxthreads support for riscv64 was added to uClibc-ng.
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>