Problems building & testing node.js 7.x.x from source - node.js

Question

I'm desperately trying to install node.js (6.10.0, 7.5.0, 7.6.0, 7.7.1) from source onto my server.
First, I get several warnings about compares between signed & unsigned ints (mainly in the deps/icu- and deps/v8-folder). However, make ends successfully. I'm using gcc 6.2.
"make test" ends successfully, too - except one single test addressing "sequential/test-debug-host-port".
"make test-npm" has most problems. If I run it under root I get 39 tests failing. However, running under a normal user there's only one test failing:
0 info it worked if it ends with ok
1 verbose cli [ '/xxxxx/node-v7.7.1/out/Release/node',
1 verbose cli '/xxxxx/node-v7.7.1/test-npm/cli.js',
1 verbose cli 'run-script',
1 verbose cli 'test-node' ]
2 info using npm#4.1.2
3 info using node#v7.7.1
4 verbose run-script [ 'pretest-node', 'test-node', 'posttest-node' ]
5 info lifecycle npm#4.1.2~pretest-node: npm#4.1.2
6 silly lifecycle npm#4.1.2~pretest-node: no script for pretest-node, continuing
7 info lifecycle npm#4.1.2~test-node: npm#4.1.2
8 verbose lifecycle npm#4.1.2~test-node: unsafe-perm in lifecycle true
9 verbose lifecycle npm#4.1.2~test-node: PATH: /xxxxx/node-v7.7.1/test-npm/bin/node-gyp-bin:/xxxxx/node-v7.7.1/test-npm/node$
10 verbose lifecycle npm#4.1.2~test-node: CWD: /xxxxx/node-v7.7.1/test-npm
11 silly lifecycle npm#4.1.2~test-node: Args: [ '-c',
11 silly lifecycle 'tap --timeout 240 "test/tap/*.js" "test/network/*.js" "test/broken-under-nyc*/*.js"' ]
12 silly lifecycle npm#4.1.2~test-node: Returned: code: 1 signal: null
13 info lifecycle npm#4.1.2~test-node: Failed to exec test-node script
14 verbose stack Error: npm#4.1.2 test-node: `tap --timeout 240 "test/tap/*.js" "test/network/*.js" "test/broken-under-nyc*/*.js$
14 verbose stack Exit status 1
14 verbose stack at EventEmitter.<anonymous> (/xxxxx/node-v7.7.1/test-npm/lib/utils/lifecycle.js:279:16)
14 verbose stack at emitTwo (events.js:106:13)
14 verbose stack at EventEmitter.emit (events.js:194:7)
14 verbose stack at ChildProcess.<anonymous> (/xxxxx/node-v7.7.1/test-npm/lib/utils/spawn.js:40:14)
14 verbose stack at emitTwo (events.js:106:13)
14 verbose stack at ChildProcess.emit (events.js:194:7)
14 verbose stack at maybeClose (internal/child_process.js:899:16)
14 verbose stack at Process.ChildProcess._handle.onexit (internal/child_process.js:226:5)
15 verbose pkgid npm#4.1.2
16 verbose cwd /xxxxx/node-v7.7.1/test-npm
17 error Linux 2.6.27.56-0.1-default
18 error argv "/xxxxx/node-v7.7.1/out/Release/node" "/xxxxx/node-v7.7.1/test-npm/cli.js" "run-script" "test-node"
19 error node v7.7.1
20 error npm v4.1.2
21 error code ELIFECYCLE
22 error npm#4.1.2 test-node: `tap --timeout 240 "test/tap/*.js" "test/network/*.js" "test/broken-under-nyc*/*.js"`
22 error Exit status 1
23 error Failed at the npm#4.1.2 test-node script 'tap --timeout 240 "test/tap/*.js" "test/network/*.js" "test/broken-under-nyc*$
23 error Make sure you have the latest version of node.js and npm installed.
23 error If you do, this is most likely a problem with the npm package,
23 error not with npm itself.
23 error Tell the author that this fails on your system:
23 error tap --timeout 240 "test/tap/*.js" "test/network/*.js" "test/broken-under-nyc*/*.js"
23 error You can get information on how to open an issue for this project with:
23 error npm bugs npm
23 error Or if that isn't available, you can get their info via:
23 error npm owner ls npm
23 error There is likely additional logging output above.
24 verbose exit [ 1, true ]
I googled around and all I found was an info about non-resolvable localhost. However, localhost and 127.0.0.1 just work fine with other software on my system...