• depend on NTL: this is mandatory for SageMath, but if some users want a lighter package, I set it as an option.

• upgrade to the latest 4.1.3: it builds with 4.1.2 but 4.1.3 is said as fixing some errors seen in SageMath.

• since I was here, remove the OPTFLAGS.

PR: 245897
Submitted by: /me
Approved by: yuri (maintainer)