c: fix check for stdc, prevent conflicts with orc
c: fix check for stdc, prevent conflicts with orc

ahmedammar/platform_external_gst_liborc,Distrotech/orc,ijsf/OpenWebRTC-orc,MOXfiles/orc,mojaves/orc,okuoku/nmosh-orc,ahmedammar/platform_external_gst_liborc,mojaves/orc,jpakkane/orc,ijsf/OpenWebRTC-orc,ijsf/OpenWebRTC-orc,jpakkane/orc,okuoku/nmosh-orc,Distrotech/orc,okuoku/nmosh-orc,MOXfiles/orc,MOXfiles/orc,jpakkane/orc,mojaves/orc,Distrotech/orc