build: Support gcc-10 compilation on Unikraft

build: Support gcc-10 compilation on Unikraft

When compiling Unikraft with gcc-10, the compiler replace the memset
function with a recursive builtin memset call, which result in a
infinite recursive call to the memset causing exhaustion of the stack
memory eventually leading to crash. To fix this the gcc provides
compiler flags -ffreestanding and -fhosted.

Signed-off-by: Sharan Santhanam <sharan.santhanam@neclab.eu>
Reviewed-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@upb.ro>