Set make jobs to number of CPUs (#627)
Set make jobs to number of CPUs (#627)

This change is imported from rbenv, originally the work of:

- Mislav Marohnić @mislav: https://github.com/rbenv/ruby-build/commit/6c08c56d3aa0add92c60653744324e7cdb3b24c3 https://github.com/rbenv/ruby-build/commit/f4c2fe67e3b8f2f2304ce75beaa54bc5b3cb5371
- Kjetil Limkjær @klimkjar: https://github.com/rbenv/ruby-build/commit/6d6725a8a26ac6be8bdd1fbf97f96efa296d90e5
- Ville Skyttä @scop: https://github.com/rbenv/ruby-build/commit/67c47603ee4cd86550bf0a0069a0a45b02057c7c


Co-authored-by: mislav <54368f648c09f5f4adbb3f78e9119e1db33dac39@users.noreply.github.com>
Co-authored-by: klimkjar <bbe890080eca4c2c949d1f5e338d508b715e0f17@users.noreply.github.com>
Co-authored-by: scop <31201322e4a1ef11bd8e70de5ad3214b7a1b77ac@users.noreply.github.com>
Co-authored-by: smola <8b0dafe15a2d887b3916c3fdd4acc054f0358d33@users.noreply.github.com>

gerardroche/php-build,php-build/php-build