Revert r277966. Forgot patch attribution.

llvm-svn: 277967
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: faf3149df62ab1f98e21526b68686a7c62a11062
diff --git a/include/regex b/include/regex
index 42f3dbb..b223e63 100644
--- a/include/regex
+++ b/include/regex
@@ -147,7 +147,7 @@
     // construct/copy/destroy:
     basic_regex();
     explicit basic_regex(const charT* p, flag_type f = regex_constants::ECMAScript);
-    basic_regex(const charT* p, size_t len, flag_type f = regex_constants::ECMAScript);
+    basic_regex(const charT* p, size_t len, flag_type f);
     basic_regex(const basic_regex&);
     basic_regex(basic_regex&&) noexcept;
     template <class ST, class SA>
@@ -2519,7 +2519,7 @@
           __end_(0)
         {__parse(__p, __p + __traits_.length(__p));}
     _LIBCPP_INLINE_VISIBILITY
-    basic_regex(const value_type* __p, size_t __len, flag_type __f = regex_constants::ECMAScript)
+    basic_regex(const value_type* __p, size_t __len, flag_type __f)
         : __flags_(__f), __marked_count_(0), __loop_count_(0), __open_count_(0),
           __end_(0)
         {__parse(__p, __p + __len);}