Define V8_COMPILER_IS_MSVC before first use.

In https://crrev.com/c/3764190, V8_COMPILER_IS_MSVC gets used before it
is defined, so it has no effect. Move the V8_COMPILER_IS_MSVC define up
to fix this.

Change-Id: I94c63ad2a8a7555c85730792c1f91e1285a9b77f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3774095
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82090}

src/snapshot/embedded/platform-embedded-file-writer-win.cc

@@ -15,13 +15,6 @@
 #include "src/snapshot/embedded/embedded-file-writer.h"
 #endif  // V8_OS_WIN64
 
-#if defined(V8_COMPILER_IS_MSVC)
-#include "src/flags/flags.h"
-#endif
-
-namespace v8 {
-namespace internal {
-
 // V8_CC_MSVC is true for both MSVC and clang on windows. clang can handle
 // __asm__-style inline assembly but MSVC cannot, and thus we need a more
 // precise compiler detection that can distinguish between the two. clang on
@@ -30,6 +23,13 @@ namespace internal {
 #define V8_COMPILER_IS_MSVC
 #endif
 
+#if defined(V8_COMPILER_IS_MSVC)
+#include "src/flags/flags.h"
+#endif
+
+namespace v8 {
+namespace internal {
+
 // MSVC uses MASM for x86 and x64, while it has a ARMASM for ARM32 and
 // ARMASM64 for ARM64. Since ARMASM and ARMASM64 accept a slightly tweaked
 // version of ARM assembly language, they are referred to together in Visual