Handle stack spills in ARM integrated assembler.

tests_lit/assembler/arm32/load-store.ll

+; Show that we can handle variable (i.e. stack) spills.
+
+; RUN: %p2i --filetype=asm -i %s --target=arm32 --args -Om1 \
+; RUN:   | FileCheck %s --check-prefix=ASM
+; RUN: %p2i --filetype=iasm -i %s --target=arm32 --args -Om1 \
+; RUN:   | FileCheck %s --check-prefix=IASM
+
+define internal i32 @add1ToR0(i32 %p) {
+  %v = add i32 %p, 1
+  ret i32 %v
+}
+
+; ASM-LABEL: add1ToR0:
+; IASM-LABEL: add1ToR0:
+
+; ASM:          sub     sp, sp, #8
+; IASM:         .byte 0x8
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x4d
+; IASM-NEXT:    .byte 0xe2
+
+; ASM-NEXT:     str     r0, [sp, #4]
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     ldr     r0, [sp, #4]
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x9d
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     add     r0, r0, #1
+; IASM-NEXT:    .byte 0x1
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x80
+; IASM-NEXT:    .byte 0xe2
+
+; ASM-NEXT:     str     r0, [sp]
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     ldr     r0, [sp]
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x9d
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     add     sp, sp, #8
+; IASM-NEXT:    .byte 0x8
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe2
+
+; ASM-NEXT:     bx      lr
+; IASM-NEXT:    .byte 0x1e
+; IASM-NEXT:    .byte 0xff
+; IASM-NEXT:    .byte 0x2f
+; IASM-NEXT:    .byte 0xe1
+