Let's also look at tmp_install:
(p3) killeent@devgpu047:lib (master)$ ls tmp_install/
bin  include  lib  share

tmp_install looks like a standard install directory containing binaries, header files and library files. For example, tmp_install/include/TH contains all the TH headers, and tmp_install/lib/ contains the libTH.so.1 file.
So why have this directory? It is used to compile the libraries that depend on each other. For example, the THC library depends on the TH library and its headers. This is referenced in the build shell script as arguments to the cmake command:
# install_dir is tmp_install
cmake ...
    -DTH_INCLUDE_PATH="$INSTALL_DIR/include" \
    -DTH_LIB_PATH="$INSTALL_DIR/lib" \

And indeed if we look at the THC library we built:
(p3) killeent@devgpu047:lib (master)$ ldd libTHC.so.1
    ...
    libTH.so.1 => /home/killeent/github/pytorch/torch/lib/tmp_install/lib/./libTH.so.1 (0x00007f84478b7000)
