mkvtoolnix: Assume gcc5+ doesn't need to be blacklisted

since they claim to support C++14.

multimedia/mkvtoolnix/Portfile

@@ -61,10 +61,9 @@ post-patch {
 
 # mkvtoolnix's configure tests for certain c++14 features.  Xcode 6.2 (clang 600.0.57)
 # is known to fail.  Xcode 7.2.1 (clang 700.1.81) is known to pass.  Assume 700+ is OK.
-# ToDo: test building with gcc 4.9 and later but blacklist all gcc for now
+# Assume gcc 5+ is OK.
 compiler.fallback-append macports-clang-3.7
-compiler.blacklist-append { clang < 700 } \
-    *gcc*
+compiler.blacklist-append {clang < 700} *gcc-3.* *gcc-4.*
 
 set cxx_stdlibflags {}
 if {[string match *clang* ${configure.cxx}]} {