This comes from automake, specifically from its `AM_SANITY_CHECK` macro, which is called from `AM_INIT_AUTOMAKE`, which is normally called early in `configure.ac`. The gist of this macro is:
* Check that the path to the source directory doesn't contain certain “unsafe” characters which can be hard to properly include in shell scripts makefiles.
* Check that `ls` appears to work.
* Check that a new file created in the build directory is newer than the `configure` file. If it isn't (typically because the clock on the build system is not set correctly), the build process is likely to fail because build processes usually rely on generated files having a more recent timestamp than the source files they are generated from.