You're looking for non-documentary movies about the making of real films?
Warnung vor einer heiligen Nutte a.k.a. Beware of a Holy Whore (Fassbinder, 1971) is a semi-autobiographical (but also partly fictional) portrayal of the filming of Whity in Spain.
Laissez-passer a.k.a. Safe Conduct (Tavernier, 2002) covers the creation of several 1940s French films during the German Occupation. It's based largely on Jean Aurenche's recollections. This may not qualify, as it really is a historical film about the French film industry in that time, rather than a single, specific film, but there are real films discussed and portrayed in the plot.
Badasssss! (Van Peebles, 2003) covers Melvin Van Peebles' filming of Sweet Sweetback's Baadasssss Song.
Cinema Verite (2013) is HBO's fictionalized account of the filming of the 1973 public television documentary series An American Family. (I know it's about a real TV documentary miniseries rather than a film, but I figured it was close to the idea..)
Hitchcock (Gervasi, 2012) is about the making of Psycho.
The Girl (Jarrold, 2012) is about the making of The Birds.
There are quite a few actor/director/producer biopics with scenes that portray the creation of real movies, of course, like Chaplin (Attenborough, 1992) or The Aviator (Scorsese, 2004).