depends: add shared dependency builder

See the README's in depends for documentation

depends/hosts/darwin.mk

@@ -0,0 +1,8 @@
+OSX_MIN_VERSION=10.6
+OSX_SDK_VERSION=10.7
+OSX_SDK=$(SDK_PATH)/MacOSX$(OSX_SDK_VERSION).sdk
+darwin_CC=clang -target $(host) -mmacosx-version-min=$(OSX_MIN_VERSION) --sysroot $(OSX_SDK)
+darwin_CXX=clang++ -target $(host) -mmacosx-version-min=$(OSX_MIN_VERSION) --sysroot $(OSX_SDK)
+darwin_CFLAGS=-pipe -O2
+darwin_CXXFLAGS=$(darwin_CFLAGS)
+darwin_native_toolchain=native_cctools