build: Add support for building out of tree with O=/object/output/dir

Some people prefer to have the build output be done out of tree.
This follows the Linux method of building the objects in another
path.

  make O=~/mypath

Will build the objects and the executables into the ~/mypath directory.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
1 file changed