Test which flags make our asm compile.

Previously we relied on assumption that clang always needs -no-integrated-as
but it's not always true.

asm-tests/arm.S

@@ -0,0 +1,20 @@
+/* on arm clang doesn't support .arch directive */
+
+	.text
+	.syntax	unified
+
+#if !defined (__thumb2__)
+	.arch	armv7a
+	.arm
+#else
+	.arch	armv7
+	.thumb
+#endif
+	mcr	p15, 0, r11, c7, c14, 2
+
+	/* clang restricts access to dsb/isb despite .arch  */
+	dsb
+	isb
+
+
+