The --prefix parameter differs between yasm and nasm; nasm
requires --prefix _ while yasm requires --prefix=_. Using the
define instead (as on windows) allows easier switching between
the two otherwise mostly compatible assemblers.
This fixes building with yasm on OS X in 32 bit mode. For 64 bit,
a few more tweaks are still required.
This avoids coupling the architecture directly to the platform,
allowing building on e.g. linux on architectures other than x86,
without having to explicitly specify USE_ASM=No while building
on those.
Later this will also facilitate enabling assembly optimizations
where applicable, e.g. arm assembly on linux.
This is enabled for platforms/compilers that support the -MMD
option, which creates a dependency file named out.d when compiling
to a file named out.o, only including local, not system headers.
The additional -MP option adds phony targets for all included
headers, to avoid having make error out due to "no rule to make
target foo.h" if a header is renamed/removed.
This makes sure that all the right files are rebuilt if a header
is changed, avoiding the need for a full rebuild if only a few
files are affected.
Don't enable threading globally since the MSVC/ARM build target
(neither windows phone nor windows rt) doesn't support the normal
windows threading functions.
The library uses this define to enable OS X specific functionality
in general, even if none of those snippets actually have been
strictly required so far.
