[build] Workaround for regression

This patchs adds a workaround for macOS because of the
issue where it fails to compile when _XOPEN_SOURCE is
defined to a value in [500,699]. It changes the value
to 700 to workaround the issue described below:
https://github.com/llvm/llvm-project/issues/117630

Bug: 384759999
Change-Id: I74471b7808001ae58db1c1643280b04aaf253958
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/abseil-cpp/+/1181127
Reviewed-by: Alex Pankhurst <pankhurst@google.com>
diff --git a/absl/time/internal/cctz/BUILD.gn b/absl/time/internal/cctz/BUILD.gn
index b31c328..88f2ae2 100644
--- a/absl/time/internal/cctz/BUILD.gn
+++ b/absl/time/internal/cctz/BUILD.gn
@@ -43,6 +43,12 @@
     "include/cctz/zone_info_source.h",
   ]
 
+  defines = []
+  if (is_mac) {
+    # Work-around for https://github.com/llvm/llvm-project/issues/117630
+    defines += [ "_XOPEN_SOURCE=700" ]
+  }
+
   deps = [ ":civil_time" ]
 
   if (is_fuchsia) {