Split up build.h

[randombit]

A lot of build.h is completely for internal use. It contains:

• Version information (needs to be public)
• BOTAN_MP_WORD_BITS
• Installation paths
• Path to the system cert bundle
• Definition of BOTAN_DLL (only reason that ffi.h depends on build.h is this)
• Botan target OS info / flags
• If we can use GCC inline asm
• CPU info / flags
• Valgrind toggle
• Debug asserts option
• The BOTAN_HAS_FOO list (needs to be public)
• %{local_config} (we should probably just remove this)
• Some things that are nominally editable but really should just be const size_ts in some appropriate header.

From an API perspective the only things that the user needs to see is the version info and the HAS_FOO feature macros.

Some other things probably need to be visible since we use them in headers somehow (eg BOTAN_MP_WORD_BITS defines size of word and we use that in headers)

[Shinleon]

This appears to be fixed, at least in that build.h doesn't exist, and buildh.in doesn't have BOTAN_HAS_FOO or %{local_config}.