Update min-macos to 10.9

Since XCode 10, Apple does not recommend building for macOS <10.9

Reason - 10.7 and 10.8 require libstdc++

We enforce libc++ 

```# Shouldn't cmake do this???
   string( APPEND CMAKE_CXX_FLAGS " -stdlib=libc++" )```

While this generally works, it makes the proper dependency management tricky.
 
Compiler message for the library support:

```
clang: warning: libstdc++ is deprecated; move to libc++ with a minimum deployment target of OS X 10.9 [-Wdeprecated]
    ld: library not found for -lstdc++
```

src/CMakeLists.txt

@@ -1155,7 +1155,7 @@ elseif( CMAKE_SYSTEM_NAME MATCHES "Darwin" )
    if( PLATFORM_VERSION_SUPPORTED )
       list( APPEND LDFLAGS
          PRIVATE
-            -Wl,-platform_version,macos,10.7,10.13
+            -Wl,-platform_version,macos,${MIN_MACOS_VERSION},${TARGET_MACOS_VERSION}
       )
    else()
       list( APPEND LDFLAGS