[libcxx] Portability fix: std::regex_constants::error_type values are not requied to be non-zero.

[amakc11]

Summary

The standard requires the following for the std::regex_constants::error_type values: "The type error_­type is an implementation-defined enumerated type". The values of this enumerated type are not required to be non-zero. This patch makes such checks in tests libc++-specific to let the tests pass for other conforming implementations.

test/std/re/re.const/re.err/error_type.pass.cpp

 // }
 
 #include <regex>
 #include <cassert>
 #include "test_macros.h"
 
 int main(int, char**)
 {
-    assert(std::regex_constants::error_collate != 0);
-    assert(std::regex_constants::error_ctype != 0);
-    assert(std::regex_constants::error_escape != 0);
-    assert(std::regex_constants::error_backref != 0);
-    assert(std::regex_constants::error_brack != 0);
-    assert(std::regex_constants::error_paren != 0);
-    assert(std::regex_constants::error_brace != 0);
-    assert(std::regex_constants::error_badbrace != 0);
-    assert(std::regex_constants::error_range != 0);
-    assert(std::regex_constants::error_space != 0);
-    assert(std::regex_constants::error_badrepeat != 0);
-    assert(std::regex_constants::error_complexity != 0);
-    assert(std::regex_constants::error_stack != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_collate != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_ctype != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_escape != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_backref != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_brack != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_paren != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_brace != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_badbrace != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_range != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_space != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_badrepeat != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_complexity != 0);
+    LIBCPP_ASSERT(std::regex_constants::error_stack != 0);
 
     assert(std::regex_constants::error_collate != std::regex_constants::error_ctype);
     assert(std::regex_constants::error_collate != std::regex_constants::error_escape);
     assert(std::regex_constants::error_collate != std::regex_constants::error_backref);
     assert(std::regex_constants::error_collate != std::regex_constants::error_brack);
     assert(std::regex_constants::error_collate != std::regex_constants::error_paren);
     assert(std::regex_constants::error_collate != std::regex_constants::error_brace);
     assert(std::regex_constants::error_collate != std::regex_constants::error_badbrace);