media-gfx/iscan: fix build due to bool mismatch

Use <stdbool.h> instead of a custom bool type when available, to avoid
build failures if other packages include <stdbool.h> later, which
redefines it to _Bool. This causes build failures due to mismatch
between declarations and definitions.

Closes: https://bugs.gentoo.org/755884
Package-Manager: Portage-3.0.12, Repoman-3.0.2
Signed-off-by: Hector Martin <marcan@marcan.st>
Closes: https://github.com/gentoo/gentoo/pull/18938
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>

media-gfx/iscan/files/iscan-2.30.4.2-c99.patch

@@ -0,0 +1,24 @@
+--- a/backend/defines.h	2021-01-04 08:13:48.995137756 -0000
++++ b/backend/defines.h	2021-01-04 08:16:00.524563361 -0000
+@@ -31,6 +31,13 @@
+ 
+ 
+ #ifndef __cplusplus
++
++/*  Use the C99 bool type if available
++ */
++#ifdef HAVE_STDBOOL_H
++#include <stdbool.h>
++#else
++
+ /*! A C++ Boolean type and corresponding keywords for our C code.
+  */
+ typedef enum {
+@@ -38,6 +45,7 @@
+   true
+ } bool;
+ #endif
++#endif
+ 
+ 
+ /*  Run-time contract validation.

media-gfx/iscan/iscan-2.30.4.2-r1.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2020 Gentoo Authors
+# Copyright 1999-2021 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
@@ -70,6 +70,7 @@ PATCHES=(
 	"${FILESDIR}"/iscan-2.30.1.1-gcc6.patch
 	"${FILESDIR}"/iscan-2.30.3.1-fix-x86-unknown-types.patch
 	"${FILESDIR}"/iscan-2.30.4.2-sscanf.patch
+	"${FILESDIR}"/iscan-2.30.4.2-c99.patch
 )
 
 QA_PRESTRIPPED="usr/lib.*/libesmod.so.*"