update README.md for building on OSX

[timwr]

This should work on a fresh install of OSX.
Let me know if you see this error:

Configuring mettle for x86_64-apple-darwin
configure: WARNING: unrecognized options: --disable-shared
configure: error: cannot find install-sh, install.sh, or shtool in "/Users/user/dev/git/mettle/mettle" "/Users/user/dev/git/mettle/mettle/.." "/Users/user/dev/git/mettle/mettle/../.."
make: *** [/Users/user/dev/git/mettle/build/x86_64-apple-darwin/mettle/Makefile] Error 1

[tkmru]

make TARGET=x86_64-apple-darwin is no problem on El Capitan.

[timwr]

make TARGET=i386-apple-darwin should work now

[sempervictus]

So on OSX 10.9 (last version you can install on the core2duo iMacs), -framework CoreImage needs to be -framework QuartzCore, still fighting all sorts of weird xcode/compiler problems. It seems to hate not using clang and its native pieces, all sorts of weirdness about which gcc, which ld, shtool, etc. Good god OSX is a crazy mess :).

For reference:

ProductName:	Mac OS X
ProductVersion:	10.9.5
BuildVersion:	13F1808

and

diff --git a/make/Makefile.common b/make/Makefile.common
index e3da2dc..9c3ff9e 100644
--- a/make/Makefile.common
+++ b/make/Makefile.common
@@ -16,7 +16,7 @@ DEPS=$(ROOT)/deps
 OUTPUTDIR=$(BUILD)/data
 
 ifneq (,$(findstring darwin,$(TARGET)))
-    LDFLAGS:=$(LDFLAGS) -framework Foundation -framework AVFoundation -framework CoreMedia -framework CoreImage -framework CoreVideo
+    LDFLAGS:=$(LDFLAGS) -framework Foundation -framework AVFoundation -framework CoreMedia -framework QuartzCore -framework CoreVideo
     ifneq (,$(findstring iphone,$(TARGET)))
         export SDKROOT=$(shell xcrun --sdk iphoneos --show-sdk-path)
         LDFLAGS:=$(LDFLAGS) -framework UIKit -framework CoreGraphics