Build universal architecture library for iPhone -- lipo hints

When developing a ios library for both simulator and iPhone/iPad(s),
the steps are :
1. build each architecture one by one and put into identical path, ie
build.armv6 --- armv6 library
build.armv7 --- armv7 library
build.i386 --- i386 library for simulator

2. use lipo command
lipo -create ./build.armv6/lib1.a ./build.armv7/lib1.a ./build.i386/lib1.a -output ./build.all/lib1.a

lib1.a will contain all three libraries which can be used by iPhone cross ompiler.

3. To see what archs are supported by a library, we can use
lipo -info library_file can get the supported architecture of the library

4. The iPhone/iPad family architectures :

ARMv7s = iPhone 5, iPad 4
ARMv7  = iPhone 3GS, iPhone 4, iPhone 4S, iPod 3G/4G/5G, iPad, iPad 2, iPad 3, iPad Mini  
ARMv6  = iPhone 2G/3G, iPod 1G/2G