Microoptimization of short fixed string generation

Don't use memcpy when we can do an unaligned store
Move all dialect and warning options from CFLAGS to PROJECT_CFLAGS

It should be possible to set CFLAGS as an argument to make without
having to replicate lots of options for the build to succeed.
Fix various maybe-uninitialized errors from gcc with -O6

Some of these were real bugs.  Some were due to storing uninitialized
values into the resume frame because those values were not relevant
in the current state.
Further micro-optimization of parsing of negative ints