The "l" (ell) width spec means something in the corresponding scanf usage,
but not here.  While modern POSIX says that applying "l" to "f" and other
floating format specs is a no-op, SUSv2 says it's undefined.  Buildfarm
experience says that some old compilers emit warnings about it, and at
least one old stdio implementation (mingw's "ANSI" option) actually
produces wrong answers and/or crashes.

Discussion: https://postgr.es/m/21670.1526769114@sss.pgh.pa.us
Discussion: https://postgr.es/m/c085e1da-0d64-1c15-242d-c921f32e0d5c@dunslane.net