Fix undefined "_environ" symbol link MacOSX error specific to shared build.

This commit fix the MacOSX shared build that was broken as a side effect
of the removal (commit 375f0fca) of the setresgid/setresuid hack.
Merge branch 'fix-macosx-environ-link-error'

* fix-macosx-environ-link-error:
  Fix undefined "_environ" symbol link MacOSX error specific to shared build.