Capture output of Vela and print on error (#3057)

Summary:
Change-Id: I0443a6ab26766a51511d9e4ea532fc8e76836ede

Pull Request resolved: #3057

Reviewed By: mergennachin

Differential Revision: D56476746

Pulled By: digantdesai

fbshipit-source-id: 4b6d9738a9202980fa06bb8f4232fb4a916a7633

Author: Erik-Lundell

backends/arm/arm_vela.py

@@ -43,7 +43,14 @@ def vela_compile(tosa_graph, args: List[str]):
 
         # invoke vela
         vela_command = f"cd {tmpdir}; vela {' '.join(args)} {tosaname}"
-        subprocess.run([vela_command], shell=True, check=True)
+        try:
+            subprocess.run([vela_command], shell=True, check=True, capture_output=True)
+        except subprocess.CalledProcessError as process_error:
+            raise RuntimeError(
+                f"Vela compiler ('{vela_command}') failed with error:\n \
+                                     {process_error.stderr.decode()}\n \
+                                      Stdout:\n{process_error.stdout.decode()}"
+            )
 
         np_path = os.path.join(tmpdir, "output", "out_sg0_vela.npz")
         blocks = b""