media-libs/libbpg: fix implicit declaration of string function

The patch has not yet upstreamed.

Signed-off-by: Lucio Sauer <watermanpaint@posteo.net>

media-libs/libbpg/files/libbpg-0.9.8-fix-implicit-declaration.patch

@@ -0,0 +1,13 @@
+The strrchr function prototype may have been provided transitively in the past.
+Not yet upstreamed as of 2023-09-17.
+Author: Lucio Sauer <watermanpaint@posteo.net>
+--- a/bpgdec.c
++++ b/bpgdec.c
+@@ -33,6 +33,7 @@
+ 
+ #ifdef USE_PNG
+ #include <png.h>
++#include <string.h>
+ #endif
+ 
+ #include "libbpg.h"

media-libs/libbpg/libbpg-0.9.8-r1.ebuild

@@ -37,6 +37,7 @@ PATCHES=(
 	"${FILESDIR}"/${P}-add-fpic.patch
 	"${FILESDIR}"/${P}-backport-GNU-stack-note-fix.patch
 	"${FILESDIR}"/${P}-dont-strip-bins.patch
+	"${FILESDIR}"/${P}-fix-implicit-declaration.patch
 	"${FILESDIR}"/${P}-remove-forced-options.patch
 	"${FILESDIR}"/${P}-remove-unused-cmake-var.patch
 	"${FILESDIR}"/${P}-respect-compiler-driver.patch