Split includes.

All code needs uvm32_sys.h, but uvm32_common_custom.h is optional (and has defs needed for demos)

apps/rust-hello/build.rs

@@ -6,7 +6,7 @@ fn main() {
     println!("cargo:rustc-link-arg-bin=rust-hello=-T../common/linker.ld");
 
     let bindings = bindgen::Builder::default()
-        .header("../../common/uvm32_sys.h")
+        .header("uvm32_headers.h")
         .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
         .generate()
         .expect("Unable to generate bindings");

apps/rust-hello/uvm32_headers.h

@@ -0,0 +1,2 @@
+#include "../../common/uvm32_sys.h"
+#include "../../common/uvm32_common_custom.h"

common/uvm32_common_custom.h

@@ -1,4 +1,5 @@
-// Definitions needed by both host and target
+// Syscall definitions needed by both host and target for sample apps
+// These are not required when building a custom host target code with uvm32
 
 // syscalls for exposed host functions, start at 0
 #define UVM32_SYSCALL_PUTC      0x00000000

common/uvm32_sys.h

@@ -1,8 +1,15 @@
+#ifndef UVM32_SYS_H
+#define UVM32_SYS_H 1
+
+// Common definitions used by both uvm32.c and any code running inside VM
+
 // System provided UVM32_SYSCALLs, start at 0x10000000
 #define UVM32_SYSCALL_HALT          0x1000000
 #define UVM32_SYSCALL_YIELD         0x1000001
 #define UVM32_SYSCALL_STACKPROTECT  0x1000002
 
+// Address of External RAM, when offered by host
 #define UVM32_EXTRAM_BASE 0x10000000
 
-#include "uvm32_common_custom.h"
+#endif
+