media-gfx/jpegoptim: avoid broken/dated getopt.c with musl

*Should* fix bug #944902 but lazily haven't actually tried gcc15+musl
given my ready-to-use musl chroot is llvm-musl. Did try it with glibc
and gcc-15 is fine as-is though.

Closes: https://bugs.gentoo.org/944902
Signed-off-by: Ionen Wolkens <ionen@gentoo.org>

media-gfx/jpegoptim/jpegoptim-1.5.5.ebuild

@@ -1,9 +1,9 @@
-# Copyright 1999-2023 Gentoo Authors
+# Copyright 1999-2024 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
 
-inherit cmake
+inherit cmake flag-o-matic
 
 DESCRIPTION="Utility to optimize JPEG files"
 HOMEPAGE="https://www.kokkonen.net/tjko/projects.html"
@@ -23,6 +23,8 @@ PATCHES=(
 )
 
 src_configure() {
+	use elibc_musl && append-cppflags -D__GNU_LIBRARY__ #944902
+
 	local mycmakeargs=(
 		-DUSE_MOZJPEG=no
 	)