[ARM] Avoid creating unwind annotations for FPSCR and FPEXC

Avoid annotating the saving of FPSCR and FPEXC for functions marked with the
interrupt_save_fp attribute, even though this is done as part of frame setup.
Since these are status registers, there really is no viable way of annotating
this. Since these aren't GPRs or DPRs, they can't be used with .save or .vsave
directives. Instead, just record that the intermediate registers r4 and r5 are
saved to the stack again.

Author: evodius96

clang/test/CodeGen/arm-interrupt-save-fp-attr-status-regs.c

@@ -17,15 +17,15 @@ void bar();
 __attribute__((interrupt_save_fp)) void test_generic_interrupt() {
     // CHECK-R:      vmrs	r4, fpscr
     // CHECK-R-NEXT: vmrs	r5, fpexc
-    // CHECK-R-NEXT: .save  {fpscr, fpexc}
+    // CHECK-R-NEXT: .save  {r4, r5}
     // CHECK-R-NEXT: push	{r4, r5}
     // .....
     // CHECK-R:      pop	{r4, r5}
     // CHECK-R-NEXT: vmsr	fpscr, r4
     // CHECK-R-NEXT: vmsr	fpexc, r5
 
     // CHECK-M:      vmrs	r4, fpscr
-    // CHECK-M-NEXT: .save  {fpscr}
+    // CHECK-M-NEXT: .save  {r4}
     // CHECK-M-NEXT: push	{r4}
     // .....
     // CHECK-M:      pop	{r4}

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

@@ -1380,9 +1380,10 @@ void ARMAsmPrinter::EmitUnwindingInstruction(const MachineInstr *MI) {
       case ARM::VMRS:
       case ARM::VMRS_FPEXC:
         // If a function spills FPSCR or FPEXC, we copy the values to low
-        // registers before pushing them. Record the copy so we can emit the
-        // correct ".save" later.
-        AFI->EHPrologueRemappedRegs[DstReg] = SrcReg;
+        // registers before pushing them.  However, we can't issue annotations
+        // for FP status registers because ".save" requires GPR registers, and
+        // ".vsave" requires DPR registers, so don't record the copy and simply
+        // emit annotations for the source registers used for the store.
         break;
       case ARM::tLDRpci: {
         // Grab the constpool index and check, whether it corresponds to