Can't build with MacOSX

[remoe]

I've tried to build the MacOSX binary.

cmake -H. -Bbuild -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_PREFIX_PATH=/usr/local/opt/qt5 

The compiler errors was:

apitrace/retrace/glws_cocoa.mm:117:30: error: use of undeclared identifier 'NSWindowStyleMaskTitled'
                  styleMask: NSWindowStyleMaskTitled |
                             ^
apitrace/retrace/glws_cocoa.mm:118:46: error: use of undeclared identifier 'NSWindowStyleMaskClosable'
                                             NSWindowStyleMaskClosable |
                                             ^
apitrace/retrace/glws_cocoa.mm:119:46: error: use of undeclared identifier 'NSWindowStyleMaskMiniaturizable'
                                             NSWindowStyleMaskMiniaturizable
                                             ^
apitrace/retrace/glws_cocoa.mm:345:46: error: use of undeclared identifier 'NSEventMaskAny'
        event = [NSApp nextEventMatchingMask:NSEventMaskAny

To fix this, one can insert this with a MacOSX SDK version prefix:

file: glws_cocoa.mm

#define NSWindowStyleMaskTitled NSTitledWindowMask
#define NSWindowStyleMaskClosable NSClosableWindowMask
#define NSWindowStyleMaskMiniaturizable NSMiniaturizableWindowMask
#define NSEventMaskAny NSAnyEventMask

[jrfonseca]

This is due to change fe61fd0. By fixing Xcode 8.2 warnings it seems like the build for older Xcode versions broke.

Given Xcode 8.2 is publicly available and a free upgrade, I think it's ok to require it. I'll update the apitrace build to explicitly require Xcode 8.2 and abort when it's not available.