[regex] Use distinct __regex_word on NetBSD

NetBSD defines character classes up to 0x2000.  Use 0x8000 as a safe
__regex_word that hopefully will not collide with other values
in the foreseeable future.

Differential Revision: https://reviews.llvm.org/D55657

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@349293 91177308-0d34-0410-b5e6-96231b3b80d8

include/regex

@@ -990,6 +990,10 @@ public:
 
 #if defined(__mips__) && defined(__GLIBC__)
     static const char_class_type __regex_word = static_cast<char_class_type>(_ISbit(15));
+#elif defined(__NetBSD__)
+    // NetBSD defines classes up to 0x2000
+    // see sys/ctype_bits.h, _CTYPE_Q
+    static const char_class_type __regex_word = 0x8000;
 #else
     static const char_class_type __regex_word = 0x80;
 #endif