#45 Cinelerra 7 fix for compiler warning in genrand.c

[Mat Nieuwenhoven]

System Mint 18.3 (base: Ubuntu 16.04), 64 bit, AMD cpu, compiler 5.4.0 . The compiler gives warnings on the file about "incompatible implicit declaration of built-in function". This patch fixes it. Apply as "patch -p1 <genrand.c.patch" in the thirdparty/esound directory.