Fix V8 snapshot build for 32-bit Win/cross

This CL includes a revert of [1] with thakis@'s proposed fix at [2].  Verified a
build with the below gn args works on Linux:

target_os = "win"
target_cpu = "x86"
is_debug = false
is_official_build = true
is_component_build = false
use_goma = true
enable_nacl = false
use_custom_libcxx = true

[1] https://chromium.googlesource.com/v8/v8.git/+/93ee541417b6f5904072c0ecdfc6fc041811b489
[2] https://bugs.chromium.org/p/chromium/issues/detail?id=942347#c2

BUG=chromium:942347
R=machenbach
CC=thakis

Change-Id: I34f5744a9f600efbc075f4b5ba8d1c66bff46ae6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1529250
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60349}

BUILD.gn

@@ -3581,6 +3581,8 @@ if (v8_use_snapshot && current_toolchain == v8_snapshot_toolchain) {
 
     if (target_os == "fuchsia") {
       defines = [ "V8_TARGET_OS_FUCHSIA" ]
+    } else if (target_os == "win") {
+      defines = [ "V8_TARGET_OS_WIN" ]
     }
   }
 }

gni/v8.gni

@@ -37,10 +37,9 @@ declare_args() {
 
   # Enable the snapshot feature, for fast context creation.
   # https://v8.dev/blog/custom-startup-snapshots
-  # TODO(thakis): Make snapshots work in 64-bit win/cross builds
-  # (https://crbug.com/803591) and 32-bit win/cross builds
-  # (https://crbug.com/942347)
-  v8_use_snapshot = !is_win || host_os == "win"
+  # TODO(thakis): Make snapshots work in 64-bit win/cross builds,
+  # https://803591
+  v8_use_snapshot = !(is_win && host_os != "win" && target_cpu == "x64")
 
   # Enable several snapshots side-by-side (e.g. default and for trusted code).
   v8_use_multi_snapshots = false

src/snapshot/embedded-file-writer.cc

@@ -41,7 +41,7 @@ namespace internal {
 
 // Name mangling.
 // Symbols are prefixed with an underscore on 32-bit architectures.
-#if defined(V8_OS_WIN) && !defined(V8_TARGET_ARCH_X64) && \
+#if defined(V8_TARGET_OS_WIN) && !defined(V8_TARGET_ARCH_X64) && \
     !defined(V8_TARGET_ARCH_ARM64)
 #define SYMBOL_PREFIX "_"
 #else
@@ -65,7 +65,7 @@ DataDirective PointerSizeDirective() {
 }  // namespace
 
 const char* DirectiveAsString(DataDirective directive) {
-#if defined(V8_OS_WIN) && defined(V8_ASSEMBLER_IS_MASM)
+#if defined(V8_TARGET_OS_WIN) && defined(V8_ASSEMBLER_IS_MASM)
   switch (directive) {
     case kByte:
       return "BYTE";
@@ -76,7 +76,7 @@ const char* DirectiveAsString(DataDirective directive) {
     default:
       UNREACHABLE();
   }
-#elif defined(V8_OS_WIN) && defined(V8_ASSEMBLER_IS_MARMASM)
+#elif defined(V8_TARGET_OS_WIN) && defined(V8_ASSEMBLER_IS_MARMASM)
   switch (directive) {
     case kByte:
       return "DCB";
@@ -432,10 +432,10 @@ int PlatformDependentEmbeddedFileWriter::IndentedDataDirective(
   return fprintf(fp_, "  %s ", DirectiveAsString(directive));
 }
 
-// V8_OS_WIN (MSVC)
+// V8_TARGET_OS_WIN (MSVC)
 // -----------------------------------------------------------------------------
 
-#elif defined(V8_OS_WIN) && defined(V8_ASSEMBLER_IS_MASM)
+#elif defined(V8_TARGET_OS_WIN) && defined(V8_ASSEMBLER_IS_MASM)
 
 // For MSVC builds we emit assembly in MASM syntax.
 // See https://docs.microsoft.com/en-us/cpp/assembler/masm/directives-reference.
@@ -566,7 +566,7 @@ int PlatformDependentEmbeddedFileWriter::IndentedDataDirective(
 
 #undef V8_ASSEMBLER_IS_MASM
 
-#elif defined(V8_OS_WIN) && defined(V8_ASSEMBLER_IS_MARMASM)
+#elif defined(V8_TARGET_OS_WIN) && defined(V8_ASSEMBLER_IS_MARMASM)
 
 // The the AARCH64 ABI requires instructions be 4-byte-aligned and Windows does
 // not have a stricter alignment requirement (see the TEXTAREA macro of
@@ -692,7 +692,7 @@ void PlatformDependentEmbeddedFileWriter::SectionData() {
 }
 
 void PlatformDependentEmbeddedFileWriter::SectionRoData() {
-#if defined(V8_OS_WIN)
+#if defined(V8_TARGET_OS_WIN)
   fprintf(fp_, ".section .rdata\n");
 #else
   fprintf(fp_, ".section .rodata\n");
@@ -779,7 +779,7 @@ void PlatformDependentEmbeddedFileWriter::DeclareFunctionBegin(
     const char* name) {
   DeclareLabel(name);
 
-#if defined(V8_OS_WIN)
+#if defined(V8_TARGET_OS_WIN)
 #if defined(V8_TARGET_ARCH_ARM64)
   // Windows ARM64 assembly is in GAS syntax, but ".type" is invalid directive
   // in PE/COFF for Windows.