security/libtasn1: add a workaround for clang 10+
When compiled with clang 10+ and -O[2-9], the resulting package
fails to parse certificates.
As a workaround, downgrade optimization to -O1.
Upstream issue: https://gitlab.com/gnutls/libtasn1/-/issues/30
PR: 252548
Reported by: rozhuk.im@gmail.com