lib: log any errors when creating Python symlink

Warn users about errors, but continue on in case the user does
happen to have new enough Python on their PATH.

(The symlinks are only meant to fix an issue in a corner case,
where the user told `node-gyp` where new enough Python is,
but it's not the first `python3` on their PATH.
We should not introduce a new potential failure mode to all users
when fixing this bug. So no hard errors during the symlink process.)

Author: DeeDeeG

lib/configure.js

@@ -95,8 +95,15 @@ function configure (gyp, argv, callback) {
 
     log.verbose('python symlink', `creating symlink to "${python}" at "${symlinkDestination}"`)
 
-    fs.unlink(symlinkDestination, function () {
-      fs.symlink(python, symlinkDestination, function () {})
+    fs.unlink(symlinkDestination, function (err) {
+      if (err && err.code !== 'ENOENT') {
+        log.warn('python symlink', 'error when attempting to remove existing symlink\n', err)
+      }
+      fs.symlink(python, symlinkDestination, function (err) {
+        if (err) {
+          log.warn('python symlink', 'error when attempting to create Python symlink\n', err)
+        }
+      })
     })
   }