Import of CCTZ from GitHub.

PiperOrigin-RevId: 501343076
Change-Id: I12e04a87b9a90951f9b52bd9690cce28d03b0f29

absl/time/internal/cctz/src/zone_info_source.cc

diff --git a/absl/time/internal/cctz/src/zone_info_source.cc b/absl/time/internal/cctz/src/zone_info_source.cc
index b818c21..1b16233 100644
--- a/absl/time/internal/cctz/src/zone_info_source.cc
+++ b/absl/time/internal/cctz/src/zone_info_source.cc
@@ -58,7 +58,8 @@
 // MinGW is GCC on Windows, so while it asserts __has_attribute(weak), the
 // Windows linker cannot handle that. Nor does the MinGW compiler know how to
 // pass "#pragma comment(linker, ...)" to the Windows linker.
-#if (__has_attribute(weak) || defined(__GNUC__)) && !defined(__MINGW32__)
+#if (__has_attribute(weak) || defined(__GNUC__)) && !defined(__MINGW32__) && \
+    !defined(__CYGWIN__)
 ZoneInfoSourceFactory zone_info_source_factory __attribute__((weak)) =
     DefaultFactory;
 #elif defined(_MSC_VER) && !defined(__MINGW32__) && !defined(_LIBCPP_VERSION)