[libc++] Relax libc++-only test on regex_constants

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.

Thanks to Andrey Maksimov for the patch.
Differential Revision: https://reviews.llvm.org/D61195

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@359320 91177308-0d34-0410-b5e6-96231b3b80d8

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

@@ -37,19 +37,19 @@
 
 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);