add -F option to specify {C,A,LD}FLAGS for build
missing -D_FILE_OFFSET_BITS=64 on i386 and arm
factor out setting -D_FILE_OFFSET_BITS=64 for 32 bit platforms
factor out -fPIC setting for MIPS
factor out setting of env vars that MIPS ABIs need
only add -m32 or -m64 if necessary, as may be set with -F
MIPS n32 not yet working
travis does not like \ any more...
add -F ALLFLAGS= option
remove -32/-64 flags
tweak MIPS handling
update Changelog for flags changes
use ACLFLAGS not ALLFLAGS for consistency