Define crc32 intrinsic builtin for gcc

This will fix the build for gcc@aarch64, enabling building V8
with gcc for aarch64.

Bug: 1066302
Change-Id: I4818d6384553a877f6c1c240b7f0c66c8db69b1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315440
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792504}

diff --git a/third_party/zlib/contrib/optimizations/insert_string.h b/third_party/zlib/contrib/optimizations/insert_string.h
index d3bc33c..9f634ae 100644
--- a/third_party/zlib/contrib/optimizations/insert_string.h
+++ b/third_party/zlib/contrib/optimizations/insert_string.h

@@ -28,11 +28,15 @@
 #elif defined(CRC32_ARMV8_CRC32)
   #if defined(__clang__)
     #define __crc32cw __builtin_arm_crc32cw
+  #elif defined(__GNUC__)
+    #define __crc32cw __builtin_aarch64_crc32cw
   #endif
 
-  #if defined(__aarch64__)
+  #if defined(__aarch64__) && defined(__clang__)
     #define TARGET_CPU_WITH_CRC __attribute__((target("crc")))
-  #else  // !defined(__aarch64__)
+  #elif defined(__aarch64__) && defined(__GNUC__)
+    #define TARGET_CPU_WITH_CRC __attribute__((target("+crc")))
+  #elif defined(__clang__) // !defined(__aarch64__)
     #define TARGET_CPU_WITH_CRC __attribute__((target("armv8-a,crc")))
   #endif  // defined(__aarch64__)