We use these flags in our test-security-check make target, but they are
only available because debian patches them in.
We can patch them in for our Guix builds so that we can check the sanity
of our security/symbol checking suite before running them.
Support for riscv64 in glibc landed in 2.27 so it's unavoidable that we
use 2.27.
Running a Bitcoin build with toolchains based on 2.24 for platforms
other than riscv64 seem to produce binaries which do not have 2.17
symbols. So use 2.24 since it's more recent and maintained by Debian
Stretch.
When building nsis, if VERSION is not specified, it defaults to
cvs_version which is non-deterministic as it includes the current date.
This patches nsis to default to SOURCE_DATE_EPOCH if it exists so that
nsis is reproducible.
Upstream change: https://github.com/kichik/nsis/pull/13
Carl Dong