jamvm: add patch to fix musl build

Add a patch available from JamVM's bug tracker to fix the build with
the musl C library. The build was verified with the musl and uClibc C
libraries.

Fixes:

  http://autobuild.buildroot.org/results/8292973e9f6f2971d090f02f24d11a31709254cf/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>