userland: add assembly support

Move arm assembly cheat here, and start some work on x86 cheat as well.

userland/arch/arm/adr.S

@@ -0,0 +1,33 @@
+/* https://github.com/cirosantilli/arm-assembly-cheat#adr */
+
+#include "common.h"
+
+.data
+data_label:
+    .word 0x1234678
+ENTRY
+    adr r0, label
+    /* objdump tells us that this uses the literal pool,
+     * it does not get converted to adr, which is the better
+     * alternative here.
+     */
+    adr r1, label
+    adrl r2, label
+label:
+    ASSERT_EQ_REG(r0, r1)
+    ASSERT_EQ_REG(r0, r2)
+
+#if 0
+    /* Error: symbol .data is in a different section.
+     *
+     * It works however in ARMv8.
+     * I think this means that there is no relocation type
+     * that takes care of this encoding in ARMv8, but there
+     * is one in ARMv8.
+     *
+     * If you have no idea what I'm talking about, read this:
+     * https://stackoverflow.com/questions/3322911/what-do-linkers-do/33690144#33690144
+     */
+    adr r1, data_label
+#endif
+EXIT