[LIB REQUEST]: GNU Scientific Library

### Library name

GNU Scientific Library (GSL)

### Library description

The GNU Scientific Library is a C library of mathematical algorithms and special functions, commonly used in scientific and numerical computing applications.

### Library repository

https://www.gnu.org/software/gsl/

### Motivation

I am a physicist. I love Compiler Explorer and I use it often to understand how my code works and how to make it faster! However, much of my code uses the GNU Scientific Library special functions and numerical integration routines, and currently this library is not known to Compiler Explorer.

No source files, tests, or entry points are identified in the issue. First inspect how Compiler Explorer exposes third-party C libraries, then review the GNU Scientific Library documentation and verify that its special functions and numerical integration routines are available in Compiler Explorer.

Written by the indexing model from the issue text.