Revert "Rename programs to instruction_processors (#3789)" (#3824)

This reverts commit 34344982a9.

programs/bpf/c/src/struct_ret/struct_ret.c

@@ -0,0 +1,21 @@
+#include <solana_sdk.h>
+
+struct test_struct { uint64_t x; uint64_t y; uint64_t z;};
+
+static struct test_struct __attribute__ ((noinline)) test_function(void) {
+  struct test_struct s;
+  s.x = 3;
+  s.y = 4;
+  s.z = 5;
+  return s;
+}
+
+extern bool entrypoint(const uint8_t* input) {
+  struct test_struct s = test_function();
+  sol_log("foobar");
+  if (s.x + s.y + s.z == 12 ) {
+    return true;
+  }
+  return false;
+}
+