Add and use COMPILE variable. Add VPATH support to build outside source dir.
Add and use COMPILE variable.
Add VPATH support to build outside source dir.

Distrotech/libsrtp,ksophocleous/libsrtp,yarrcc/libsrtp-ios,cuijinquan/libsrtp,Distrotech/libsrtp,cuijinquan/libsrtp,yarrcc/libsrtp-ios,ksophocleous/libsrtp,cuijinquan/libsrtp,persmule/libsrtp,persmule/libsrtp,persmule/libsrtp,yarrcc/libsrtp-ios