Added DESTDIR convention and exec option on Makefile

[samuelololol]

I would like to complete the DESTDIR feature and exec option to Makefile

[langston-barrett]

Sorry, I'm not super familiar with Makefiles. Could you clarify what exactly this does?

[samuelololol]

These two features actually are coming from
pote/gpm@f24ee23
pote/gpm@4e0b59a
and I think it will be very helpful when I package them into build files.

To enable DESTDIR feature in Makefile to help user to decided installed location when make install.

Although it is possible to use prefix argument with ./configure to workaround, but it makes more complicated when I trying to sandbox with packaged-gvp(sandbox location is different from prefix value, and I have to find another approach to accomplish this case instead of directly using DESTDIR value.) This is what I suffer now.

Also, $exec helps to avoid name conflicts.

Finally, after using modified Makefile, the command line output will looks like:

$ ./configure --prefix=/test_out
configuring godeps...
prefix=/test_out
>> config.make

$ make DESTDIR=./I_AM_DESTDIR/ exec=haha install
install -d ./I_AM_DESTDIR/test_out/bin
install -m 0755 ./bin/gvp ./I_AM_DESTDIR/test_out/bin/haha

$ tree I_AM_DESTDIR
I_AM_DESTDIR
└── test_out
    └── bin
        └── haha

2 directories, 1 file

[langston-barrett]

Awesome. I'll test this today, thanks for your submission and explanation!