Fix undefined behavior in syntax_option_type::operator~ and match_flag_type::operator./a.out  Found by UBSan

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@177693 91177308-0d34-0410-b5e6-96231b3b80d8

include/regex

diff --git a/include/regex b/include/regex
index 1156a3e..d1afa54 100644
--- a/include/regex
+++ b/include/regex
@@ -764,7 +764,7 @@
 syntax_option_type
 operator~(syntax_option_type __x)
 {
-    return syntax_option_type(~int(__x));
+    return syntax_option_type(~int(__x) & 0x1FF);
 }
 
 inline _LIBCPP_INLINE_VISIBILITY
@@ -840,7 +840,7 @@
 match_flag_type
 operator~(match_flag_type __x)
 {
-    return match_flag_type(~int(__x));
+    return match_flag_type(~int(__x) & 0x0FFF);
 }
 
 inline _LIBCPP_INLINE_VISIBILITY