add m68k, SuperH, and additional arm targets; bug fixes

[ghost]

• Added targets armv4t, armv5te, armv6, i486, m68k, powerpcle, sh2, sh2be, sh2-fdpic, sh2be-fdpic, sh4, and sh4be. I chose the XGCCARGS values based on what's done by richfelker/musl-cross-make:litecross/Makefile and the compilers hosted at musl.cc. I'm pretty sure that these new targets are ABI-compliant as they run correctly under qemu, but I don't have physical hardware to test these on so the XGCCARGS variables might need to be tweaked a little.
• Fixed #24 without breaking #18, since the double-space between the hash and the filename is required for b3sum, but incompatible with the openssl hash checking method (which I also moved to a new function, osslchecksum(), for clarity). Now, instead of reading STDIN, checksum() takes two command line arguments which it passes to whichever hashing function correctly.

[firasuke]

Thanks for your contribution @awbtux!

Looks good for now, will require further testing later to ensure there aren't any broken ABIs for the newly added architectures.

Merged!

[ghost]

Yeah, I'll do more testing tomorrow—I already noticed that the 32-bit little-endian powerpc architecture I added was missing the --enable-secureplt and --without-long-double-128 flags. I'll push another PR fixing whatever issues I find here.