Applied fix contributed by Greg King.

The code
  void foo(void)
  {
    int i;
    long l = 1L * i;
  }
triggered an
  Internal compiler error:
  Code generation messed up: StackPtr is -4, should be -2

Greg King: "We are lucky that the bug is simple -- a missing "else".  The result is that the compiler thinks that it does the opposite of what it actually does:  It thinks that it pushes the non-constant expression onto the stack. It doesn't; so, cc65's stack pointer is wrong."
Removed option from usage.

The option in question was removed with https://github.com/oliverschmidt/cc65/commit/37c492b544dec2460fc2c16a3d66275cc0d4edc0
Added optimizer fix originating from Ullrich von Bassewitz prepared by Greg King.
comment and formatting fixes
rename LOWDATA segment to LOWBSS
Merge pull request #54 from groessler/something_to_pull

some cleanups for 'atarixl'
Rename 'syschk' symbol in the linker config file, which forces inclusion
of the 'system check' load chunki, to '__SYSTEM_CHECK__'.
atari-asm.cfg linker config file
Put EXE header and main chunk load header into a single file --
it makes no sense to be able to include/exclude them separately.
Merge pull request #56 from groessler/something_to_pull

atari-asm.cfg
Force inclusion of 'shadow RAM preparation' load chunk in crt0.s and
not in the linker config file.
Merge pull request #58 from groessler/something_to_pull

another small atarixl change
Merge remote-tracking branch 'upstream/master'