x11-wm/river: Fix glib Undefined symbol "environ"

Cherry pick upstream 8a1afd94ca4 that fixes a runtime issue:

$ /usr/local/bin/river
ld-elf.so.1: /usr/local/lib/libglib-2.0.so.0: Undefined symbol "environ"

PR: 295804
Approved by: lwhsu (mentor, implicitly)