patch __libcpp_tzdb_directory to allow use on osx

Author: h-vetinari

libcxx/src/experimental/tzdb.cpp

@@ -48,11 +48,7 @@ namespace chrono {
 // This function is weak so it can be overriden in the tests. The
 // declaration is in the test header test/support/test_tzdb.h
 _LIBCPP_WEAK string_view __libcpp_tzdb_directory() {
-#if defined(__linux__)
   return "/usr/share/zoneinfo/";
-#else
-#  error "unknown path to the IANA Time Zone Database"
-#endif
 }
 
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