Introduce a new crypto/ directory that will (eventually) contain
all the cryptographic related code. This initially defines a
wrapper for initializing gnutls and for computing hashes with
gnutls. The former ensures that gnutls is guaranteed to be
initialized exactly once in QEMU regardless of CLI args. The
block quorum code currently fails to initialize gnutls so it
only works by luck, if VNC server TLS is not requested. The
hash APIs avoids the need to litter the rest of the code with
preprocessor checks and simplifies callers by allocating the
correct amount of memory for the requested hash.
Backports commit ddbb0d09661f5fce21b335ba9aea8202d189b98e from qemu
ARM and probably the rest of the arches have significant memory leaks as
they have no release interface.
Additionally, DrMemory does not have 64-bit support and thus I can't
test the 64-bit version under Windows. Under Linux valgrind supports
both 32-bit and 64-bit but there are different macros and code for Linux
and Windows.
