groff: fix build on Darwin (#507771)

commit e49b934b77a76443005f92a737dae7370b50e5f7

Author: G. Branden Robinson <g.branden.robinson@gmail.com>

Date:   Tue Jan 23 19:39:03 2024 -0600

    [libgroff]: Fix underspecified getenv() prototype.

    * src/libs/libgroff/getopt.c: Do it.  Seen when building groff on a

      non-glibc-based system (clang 17 complains).

---

Link: https://lists.libreplanet.org/archive/html/groff-commit/2024-01/msg00103.html

diff --git a/src/libs/libgroff/getopt.c b/src/libs/libgroff/getopt.c

index 6d4ee5b3a..77f8da1ed 100644

--- a/src/libs/libgroff/getopt.c

+++ b/src/libs/libgroff/getopt.c

@@ -124,7 +124,7 @@ static struct _getopt_data getopt_data;

    whose names are inconsistent.  */

 #ifndef getenv

-extern char *getenv ();

+extern char *getenv (const char *);

 #endif

 #endif /* not __GNU_LIBRARY__ */

    "ac_cv_path_PERL=${buildPackages.perl}/bin/perl"

    "--enable-year2038"

  ]

  ++ lib.optionals (stdenv.cc.isClang) [

    "CFLAGS=-std=gnu11" # https://github.com/NixOS/nixpkgs/pull/481765

  ]

  ++ lib.optionals (stdenv.buildPlatform != stdenv.hostPlatform) [

    "gl_cv_func_signbit=yes"

  ]