alif: Add support for building C++ user modules.

This allows alif boards to build and run `examples/usercmodule`.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

ports/alif/mcu/ensemble.ld.S

@@ -75,6 +75,14 @@ SECTIONS
     . = ALIGN(16);
   } > ROM
 
+  /* For C++ exception handling */
+  .ARM :
+  {
+    __exidx_start = .;
+    *(.ARM.exidx*)
+    __exidx_end = .;
+  } > ROM
+
   .copy.table : ALIGN(4)
   {
     __copy_table_start__ = .;

ports/alif/nosys_stubs.c

@@ -24,6 +24,7 @@
  * THE SOFTWARE.
  */
 #include <errno.h>
+#include <unistd.h>
 
 int _write(int handle, char *buffer, int size) {
     errno = ENOSYS;
@@ -44,3 +45,12 @@ int _lseek(int f, int ptr, int dir) {
     errno = ENOSYS;
     return -1;
 }
+
+pid_t _getpid(void) {
+    return 0;
+}
+
+int _kill(pid_t pid, int sig) {
+    errno = EINVAL;
+    return -1;
+}