build: look for libnode.so in lib subdirectory

[khardix]

When building with --shared, ninja will output the libnode.so into a {build_dir}/lib directory, not in the root {build_dir}. This fixes the install script to look for it in the correct place.

---

Found during review of a Fedora rpm, where we apparently been moving the libnode.so manually to the root of the build directory manually this entire time. Let's see if we can stop doing that. 😅

[khardix]

CC @richardlau FYI

[richardlau]

@khardix Unfortunately the make and ninja generators in gyp use different output directories, and this breaks non-ninja builds.
e.g.

$ tools/install.py --dest-dir /tmp/testinstl --prefix "" install
installing /tmp/testinstl/bin/node
installing /tmp/testinstl/lib/libnode.so.137
Traceback (most recent call last):
  File "/home/rlau/sandbox/github/node/tools/install.py", line 426, in <module>
    run(parse_options(sys.argv[1:]))
  File "/home/rlau/sandbox/github/node/tools/install.py", line 379, in run
    files(options, install)
  File "/home/rlau/sandbox/github/node/tools/install.py", line 185, in files
    action(options, [os.path.join(options.build_dir, 'lib', output_lib)],
  File "/home/rlau/sandbox/github/node/tools/install.py", line 84, in install
    try_copy(options, path, dest)
  File "/home/rlau/sandbox/github/node/tools/install.py", line 73, in try_copy
    return shutil.copy2(source_path, target_path)
  File "/usr/lib64/python3.9/shutil.py", line 444, in copy2
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib64/python3.9/shutil.py", line 264, in copyfile
    with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: '/home/rlau/sandbox/github/node/out/Release/lib/libnode.so.137'

Using make instead of ninja and configure --shared, I end up with:

$ find . -type f -name "libnode.so.*"
./out/Release/obj.target/libnode.so.137
./out/Release/.deps/home/rlau/sandbox/github/node/out/Release/obj.target/libnode.so.137.d
./out/Release/.deps/home/rlau/sandbox/github/node/out/Release/libnode.so.137.d
./out/Release/libnode.so.137
$

I'm not sure if there's an easy way for install.py to know whether ninja was used. If configure is passed --ninja then I believe the generated config.mk will contain

BUILD_WITH=ninja

(BUILD_WITH will not be present there at all if --ninja is NOT passed to configure).

[khardix]

Thanks for the analysis; I'll try to take another look at this next week (we have holidays in Czechia this one).

[richardlau]

Requesting changes as per #58213 (comment) (since this now has an approval).