LWG 2145 - mark constructor for std::error_category as inline and constexpr. Leave the (existing, out-of-line, non-constexpr) in the dylib for compatibility with existing programs)

llvm-svn: 188858
diff --git a/libcxx/src/system_error.cpp b/libcxx/src/system_error.cpp
index 7376b77..b40409f 100644
--- a/libcxx/src/system_error.cpp
+++ b/libcxx/src/system_error.cpp
@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define	_LIBCPP_BUILDING_SYSTEM_ERROR
 #include "system_error"
 #include "string"
 #include "cstring"