sjson module causes unresolved symbols

[jmattsson]

Expected behavior

• No unresolved symbols after linking the firmware ELF.
• Firmware build should fail if there are unresolved symbols.

Initially observed by @dnc40085 over in #1755. Historically esptool.py has bailed out if there are undefined symbols, but clearly the current version we have in our tree does not.

I have no idea why this wasn't failing horribly for @pjsg during testing...

Actual behavior

../tools/esptool.py elf2image --flash_mode dio --flash_freq 40m .output/eagle/debug/image/eagle.app.v6.out -o ../bin/
esptool.py v1.2-dev
Warning: ELF binary has undefined symbol calloc
Warning: ELF binary has undefined symbol free

Test code

Include the SJSON module in the build.

NodeMCU version

Which branch are you on? If you know the Git revision then add it here as well.
dev

Hardware

n/a

[jmattsson]

So it seems none of the functions which use calloc/free aren't actually used by the Lua module, and thus haven't caused actual problems. Now to work out why those functions are even included in the ELF after the linking...

[jmattsson]

Erk, why did we end up #includeing a .c file here?

[jmattsson]

Okay, I'm getting an appreciation for why a harsh #include was picked... curse the NON-OS SDK's non-standard include files to Hel and back sigh

[jmattsson]

Fascinating. If I build jsonsl.c into a library like everything else, things break at runtime.
Edit: Oh wait, I see why. Whoops.