[wasm] Remove 'constexpr' for gcc support

R=nicohartmann@chromium.org

Change-Id: I48294d6944c32ad6b3ee00099c682cb63ad28442
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2784685Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73640}

src/wasm/baseline/liftoff-compiler.cc

@@ -594,7 +594,8 @@ class LiftoffCompiler {
     }
   }
 
-  constexpr LiftoffRegList RegsUnusedByParams() {
+  // TODO(ahaas): Make this function constexpr once GCC allows it.
+  LiftoffRegList RegsUnusedByParams() {
     LiftoffRegList regs = kGpCacheRegList;
     for (auto reg : kGpParamRegisters) {
       regs.clear(reg);