iscan: fix build

srcpkgs/iscan/patches/c99.patch

@@ -0,0 +1,26 @@
+https://aur.archlinux.org/cgit/aur.git/commit/iscan-2.30.4.2-c99.patch?h=iscan&id=32ff91a61c0d1eb7a0a3a757cfaaa2034dd48dc1
+
+--- 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.