Fix a POSIX violation of m4 argument expansion

Maamoun TKrequested to merge
mamonet/nettle:chacha_m4_fix into master

A workaround for expanding multiple digits of argument references to QR macro in chacha-4core.asm which is incompatible with POSIX. See https://www.gnu.org/software/m4/manual/html_node/Arguments.html

Merge request reports