https://linux.die.net/man/1/gcc -- Search for `-fstrict-overflow`. And note how it says

  The -fstrict-overflow option is enabled at levels -O2, -O3, -Os. 

In other words, basically every program that you're using is compiled with that option enabled. (Release builds typically use -O2, sometimes even -O3.)

-fstrict-overflow is the opposite of what the parent comment was asking about. You want -fwrapv or -fno-strict-overflow.

I was answering the "not aware that any compilers were doing this" part, hoping that they would be able to answer their second question using the source I linked.

Basically all C and C++ compilers do this.

They do it, so they can simplify things like "x < x+1" to "true".