arch-arm: Downgrade constexpr causing build errors to const

Change-Id: Idf5ae62603b6181d44aaaef91b774fa7b26eb718
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28167
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/arch/arm/aapcs32.hh b/src/arch/arm/aapcs32.hh
index fd63483..e2e5d09 100644
--- a/src/arch/arm/aapcs32.hh
+++ b/src/arch/arm/aapcs32.hh
@@ -489,12 +489,12 @@
         if (state.variadic)
             return getArgument<Aapcs32, Float>(tc, state);
 
-        int index = state.allocate(Float{}, 1);
+        const int index = state.allocate(Float{}, 1);
 
         if (index >= 0) {
             constexpr int lane_per_reg = 16 / sizeof(Float);
-            constexpr int reg = index / lane_per_reg;
-            constexpr int lane = index % lane_per_reg;
+            const int reg = index / lane_per_reg;
+            const int lane = index % lane_per_reg;
 
             RegId id(VecRegClass, reg);
             auto val = tc->readVecReg(id);
@@ -558,14 +558,14 @@
         if (useBaseABI(state))
             return getArgument<Aapcs32, HA>(tc, state);
 
-        int base = state.allocate(Elem{}, Count);
+        const int base = state.allocate(Elem{}, Count);
         if (base >= 0) {
             constexpr int lane_per_reg = 16 / sizeof(Elem);
             HA ha;
             for (int i = 0; i < Count; i++) {
-                constexpr int index = base + i;
-                constexpr int reg = index / lane_per_reg;
-                constexpr int lane = index % lane_per_reg;
+                const int index = base + i;
+                const int reg = index / lane_per_reg;
+                const int lane = index % lane_per_reg;
 
                 RegId id(VecRegClass, reg);
                 auto val = tc->readVecReg(id);