newlib: add definitions of system, raise

Closes IDF-1220
Closes IDFGH-1811
Closes https://github.com/espressif/esp-idf/pull/4020

components/newlib/syscalls.c

@@ -21,12 +21,23 @@
 #include <sys/reent.h>
 
 
+int system(const char* str)
+{
+    errno = ENOSYS;
+    return -1;
+}
+
 int _system_r(struct _reent *r, const char *str)
 {
     __errno_r(r) = ENOSYS;
     return -1;
 }
 
+int raise(int sig)
+{
+    abort();
+}
+
 int _raise_r(struct _reent *r, int sig)
 {
     abort();

components/newlib/test/test_newlib.c

@@ -182,3 +182,8 @@ TEST_CASE("fmod and fmodf work as expected", "[newlib]")
     TEST_ASSERT_EQUAL(0.1, fmod(10.1, 2.0));
     TEST_ASSERT_EQUAL(0.1f, fmodf(10.1f, 2.0f));
 }
+
+TEST_CASE("newlib: can link 'system', 'raise'", "[newlib]")
+{
+    printf("system: %p, raise: %p\n", &system, &raise);
+}