testsuite/aarch64: Add testcae for already fixed bug [PR124078]

This big-endian testcase started to ICE with r16-7464-g560766f6e239a8
and then started to work r16-7506-g498983d9619351.
So it seems like a good idea to add the testcase for this
so it does not break again.

Pushed as obvious after a quick test to make sure it ICEd
before and it is passing now on aarch64-linux-gnu.

	PR rtl-optimization/124078

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/pr124078-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>

gcc/testsuite/gcc.target/aarch64/pr124078-1.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -mbig-endian" } */
+
+/* PR rtl-optimization/124078 */
+
+
+int __attribute__((__vector_size__(8))) v;
+void foo(int a, int b) { v = (int __attribute__((__vector_size__(8)))){a,b}; }