[Libguestfs] [PATCH nbdkit] tests: Invoke MALLOC_CHECK_ correctly and only for glibc
This is kind of horrible, but it seems to work and I can't currently
think of any better way ...
I verified that it does actually set the right environment variables
and invoke the malloc checking behaviour in glibc 2.34. I didn't test
it yet with glibc < 2.34 or !glibc.
Rich.