AIX: Fix 'may be used uninitialized' compiler errors.

    Fix additional cases where the AIX compiler reports that a variable
    may be used uninitialized.

R=titzer@chromium.org, ahaas@chromium.org, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1853703003

Cr-Commit-Position: refs/heads/master@{#35243}

src/wasm/asm-wasm-builder.cc

@@ -467,14 +467,14 @@ class AsmWasmBuilderImpl : public AstVisitor {
     }
     Type* type = expr->bounds().upper;
     if (type->Is(cache_.kAsmSigned)) {
-      int32_t i;
+      int32_t i = 0;
       if (!value->ToInt32(&i)) {
         UNREACHABLE();
       }
       byte code[] = {WASM_I32V(i)};
       current_function_builder_->EmitCode(code, sizeof(code));
     } else if (type->Is(cache_.kAsmUnsigned) || type->Is(cache_.kAsmFixnum)) {
-      uint32_t u;
+      uint32_t u = 0;
       if (!value->ToUint32(&u)) {
         UNREACHABLE();
       }