Chrono: workaround for gcc 4.6 constexpr problems

src/Chrono.hxx

@@ -20,10 +20,19 @@
 #ifndef MPD_CHRONO_HXX
 #define MPD_CHRONO_HXX
 
+#include "Compiler.h"
+
 #include <chrono>
 #include <utility>
 #include <cstdint>
 
+#if defined(__GNUC__) && !GCC_CHECK_VERSION(4,7) && !defined(__clang__)
+/* std::chrono::duration operators are "constexpr" since gcc 4.7 */
+#define chrono_constexpr gcc_pure
+#else
+#define chrono_constexpr constexpr
+#endif
+
 /**
  * A time stamp within a song.  Granularity is 1 millisecond and the
  * maximum value is about 49 days.
@@ -99,11 +108,11 @@ public:
 		return count() > 0;
 	}
 
-	constexpr SongTime operator+(const SongTime &other) const {
+	chrono_constexpr SongTime operator+(const SongTime &other) const {
 		return SongTime(*(const Base *)this + (const Base &)other);
 	}
 
-	constexpr SongTime operator-(const SongTime &other) const {
+	chrono_constexpr SongTime operator-(const SongTime &other) const {
 		return SongTime(*(const Base *)this - (const Base &)other);
 	}
 };
@@ -203,13 +212,15 @@ public:
 		return count() < 0;
 	}
 
-	constexpr SignedSongTime operator+(const SignedSongTime &other) const {
+	chrono_constexpr SignedSongTime operator+(const SignedSongTime &other) const {
 		return SignedSongTime(*(const Base *)this + (const Base &)other);
 	}
 
-	constexpr SignedSongTime operator-(const SignedSongTime &other) const {
+	chrono_constexpr SignedSongTime operator-(const SignedSongTime &other) const {
 		return SignedSongTime(*(const Base *)this - (const Base &)other);
 	}
 };
 
+#undef chrono_constexpr
+
 #endif