3BSD was released at the end of 1979 according to wikipedia, and that's just the oldest BSD source I could find, so it may have been in even older versions.
Before ANSI/ISO C I don't think there was really a "math.h" to look for - as it may be different on different systems, but as so many things derive from BSD I wouldn't be surprised if it was "de-facto" standardised to what that supported.
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According to https://unix.superglobalmegacorp.com/ it was in 3bsd libm -https://unix.superglobalmegacorp.com/cgi-bin/cvsweb.cgi/3BSD...
3BSD was released at the end of 1979 according to wikipedia, and that's just the oldest BSD source I could find, so it may have been in even older versions.
Before ANSI/ISO C I don't think there was really a "math.h" to look for - as it may be different on different systems, but as so many things derive from BSD I wouldn't be surprised if it was "de-facto" standardised to what that supported.