Your mistake is in
ffmpeg -codecs in cmd, and look in libx264:
EV libx264 libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
You'll see "EV", where "E" means Encode, "V" means Video codec. There's no "A", which means that you can't use libx264 as audio codec. Consequently
-acodec libx264 is false.
Now the answer – try to use another audio codec, e.g.
aac, the built-in AAC encoder:
ffmpeg -i recod_audio.wav -i recod_ideo.flv -c:a aac -strict -2 -c:v libx264 output.flv
ffmpeg -i recod_audio.wav -i recod_ideo.flv -c:a libmp3lame -ar 44100 -c:v libx264 output.flv