all: support [noreturn] fn abc() { for{} }, mark panic/1 and exit/1with it too. (#10654)

vlib/builtin/linux_bare/libc_impl.v

@@ -140,6 +140,7 @@ pub fn write(fd i64, buf &byte, count u64) i64 {
 	return x
 }
 
+[noreturn]
 fn bare_panic(msg string) {
 	println('V panic' + msg)
 	exit(1)
@@ -150,6 +151,7 @@ fn bare_backtrace() string {
 }
 
 [export: 'exit']
+[noreturn]
 fn __exit(code int) {
 	sys_exit(code)
 }

vlib/builtin/linux_bare/linux_syscalls.v

@@ -303,8 +303,10 @@ fn sys_execve(filename &byte, argv []&byte, envp []&byte) int {
 }
 
 // 60 sys_exit
+[noreturn]
 fn sys_exit(ec int) {
 	sys_call1(60, u64(ec))
+	for {}
 }
 
 // 102 sys_getuid