In short, there are no specific Fair Use provisions in the U.S. Constitution. The U.S. Constitution does grant Congress the power to create copyright law, but does not itself provide what the specifics of those laws may be. Separately, the Constitution protects freedom of speech.

'Fair Use' is specifically an exception to copyright law, codified in 17 USC 107, as littleadv's answer quotes. The First Amendment to the Constitution provides a general right to free speech. These are separate concepts that only sometimes overlap. Since the limits on federal government power specified in the Bill of Rights (which includes the First Amendment) are specifically intended to limit the extent of the enumerated powers of the government, in cases where protected speech and copyright law do overlap, the copyright law would need to be consistent with the First Amendment or else it would be invalid and unenforceable.

Satire may be First Amendment protected speech even when it involves no copyrighted works at all. Publications like The Onion or The Babylon Bee are full of such examples of satire that don't involve the modification or republication of anyone else's copyrighted works, for example, though plentiful examples of such works in the U.S. date back all the way to the colonial period.

Similarly, a parody of some copyrighted work may be allowed under the Fair Use exception to copyright law even if it does not involve any First Amendment concerns. For example, Weird Al Yankovic publishing a parody of some musician's song is allowed by the Fair Use exception to copyright law, but isn't necessarily First Amendment protected speech. (That is, if the Fair Use exception did not exist in copyright law, then copyright holders would most likely be able to legally prevent him from publishing parodies of their works in many cases. Granted, that doesn't really matter much in his specific case since he always gets permission anyway, though he does not legally need to.)

Of course, there are cases where the two concepts do overlap. For example, the images that changed Obama's 'Hope' campaign posters to say 'Nope' instead would be both protected free speech (political speech criticizing Obama) and also Fair Use of the copyrighted poster as parody. Though, since the First Amendment creates a Constitutional right to free speech, courts would most likely hold that copyright law could not be applied in such cases even if the Fair Use exception did not exist in codified law.

In short, there are no specific Fair Use provisions in the U.S. Constitution. The U.S. Constitution does grant Congress the power to create copyright law, but does not itself provide what the specifics of those laws may be. Specifically, the Article I, Section 8 just says, "The Congress shall have Power... To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries." Separately, the First Amendment to the Constitution protects freedom of speech.

'Fair Use' is specifically an exception to copyright law, codified in 17 USC 107, as littleadv's answer quotes. The First Amendment to the Constitution provides a general right to free speech. These are separate concepts that only sometimes overlap. Since the limits on federal government power specified in the Bill of Rights (which includes the First Amendment) are specifically intended to limit the extent of the enumerated powers of the government, in cases where protected speech and copyright law do overlap, the copyright law would need to be consistent with the First Amendment or else it would be invalid and unenforceable.

Satire may be First Amendment protected speech even when it involves no copyrighted works at all. Publications like The Onion or The Babylon Bee are full of such examples of satire that don't involve the modification or republication of anyone else's copyrighted works, for example, though plentiful examples of such works in the U.S. date back all the way to the colonial period.

Similarly, a parody of some copyrighted work may be allowed under the Fair Use exception to copyright law even if it does not involve any First Amendment concerns. For example, Weird Al Yankovic publishing a parody of some musician's song is allowed by the Fair Use exception to copyright law, but isn't necessarily First Amendment protected speech. (That is, if the Fair Use exception did not exist in copyright law, then copyright holders would most likely be able to legally prevent him from publishing parodies of their works in many cases. Granted, that doesn't really matter much in his specific case since he always gets permission anyway, though he does not legally need to.)

Of course, there are cases where the two concepts do overlap. For example, the images that changed Obama's 'Hope' campaign posters to say 'Nope' instead would be both protected free speech (political speech criticizing Obama) and also Fair Use of the copyrighted poster as parody. Though, since the First Amendment creates a Constitutional right to free speech, courts would most likely hold that copyright law could not be applied in such cases even if the Fair Use exception did not exist in codified law.