os: fix some variables not static
os: fix some variables not static

davidgranstrom/libsoundio,tresf/libsoundio,tmatth/libsoundio,tresf/libsoundio,island-org/libsoundio,bestwpw/libsoundio,tmatth/libsoundio,weizhiwu/libsoundio,andrewrk/libsoundio,island-org/libsoundio,andrewrk/libsoundio,weizhiwu/libsoundio,bestwpw/libsoundio,davidgranstrom/libsoundio