[ptr-compr] Temporarily enable double fields unboxing

We are not shipping ptr-compr in M79 on x64 because chromium:1009439
blocks 31-bit Smis on 64-bit architectures, so these's no point in
disabling double fields unboxing.

This CL will be reverted after the M79 branch point.

Bug: v8:9799, chromium:1009439
Change-Id: I28d0013d3ab06ce41d5028ba4f66c9b249de52d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1862556Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64288}

src/common/globals.h

@@ -77,7 +77,7 @@ constexpr int kStackSpaceRequiredForCompilation = 40;
 
 // Determine whether double field unboxing feature is enabled.
 #if V8_TARGET_ARCH_64_BIT && !defined(V8_COMPRESS_POINTERS)
-#define V8_DOUBLE_FIELDS_UNBOXING false
+#define V8_DOUBLE_FIELDS_UNBOXING true
 #else
 #define V8_DOUBLE_FIELDS_UNBOXING false
 #endif