This change introduces a Genode specific init function, which sets the
backend allocator used by jent_zalloc/zfree(). As consequence the
library can solely be used by native Genode components, direct libc
usage is not supported.
Fixes#2274.
This commit adds a port the jitterentropy library to Genode. As
backend on x86_{32,64} 'rdtsc' is used and on ARMv{6,7} the
performance-counter.
Fixes#1239.
