[loong64] Supplement a LoongArch support in include/v8config.h

Change-Id: I658c1b781163bcd3ca39bfceb74aef9d255247b8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3894795Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Liu Yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#83374}

include/v8config.h

@@ -703,6 +703,8 @@ V8 shared library set USING_V8_SHARED.
 #define V8_TARGET_ARCH_ARM 1
 #elif defined(__mips64)
 #define V8_TARGET_ARCH_MIPS64 1
+#elif defined(__loongarch64)
+#define V8_TARGET_ARCH_LOONG64 1
 #elif defined(_ARCH_PPC64)
 #define V8_TARGET_ARCH_PPC64 1
 #elif defined(_ARCH_PPC)