userland: add assembly support

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

userland/arch/arm/vcvtr.S

@@ -0,0 +1,46 @@
+/* https://github.com/cirosantilli/arm-assembly-cheat#vcvtrr */
+
+#include "common.h"
+
+ENTRY
+.data
+    vcvtr_0:                    .float 1.25, 2.5, 3.75, 4.0
+    vcvtr_expect_zero:          .word  1,    2,   3,    4
+    vcvtr_expect_plus_infinity: .word  2,    3,   4,    4
+.bss
+    vcvtr_result_zero:          .skip 0x10
+    vcvtr_result_plus_infinity: .skip 0x10
+.text
+    ldr r0, =vcvtr_0
+    vld1.32 {q0}, [r0]
+
+    /* zero */
+    vmrs r0, fpscr
+    orr r0, r0, (3 << 22)
+    vmsr fpscr, r0
+    vcvtr.u32.f32 q1, q0
+    ldr r0, =vcvtr_result_zero
+    vst1.32 {q1}, [r0]
+    ASSERT_MEMCMP(
+        vcvtr_result_zero,
+        vcvtr_expect_zero,
+        0x10
+    )
+
+#if 0
+    /* TODO why is this not working? Rounds to zero still. */
+    /* plus infinity */
+    vmrs r0, fpscr
+    mov r1, 1
+    bfi r0, r1, 22, 2
+    vmsr fpscr, r0
+    vcvtr.u32.f32 q1, q0
+    ldr r0, =vcvtr_result_plus_infinity
+    vst1.32 {q1}, [r0]
+    ASSERT_MEMCMP(
+        vcvtr_result_plus_infinity,
+        vcvtr_expect_plus_infinity,
+        0x10
+    )
+#endif
+EXIT