Replace .o -> .c.o or .cpp.o, .ld pattern expects source-named objects to place them into ROM instead of IRAM (which would blow up otherwise)
Check another known issue w/ newlib-4.0.0 libm which was missing remainder{,f} using existing device test code
Actually use the funcs in the resulting .elf via app_entry
Check GCC building C++ in addition to C code
Check that compiler can build and link .elf using default build flags & defines
Check for known issue w/ newlib-4.5.0 when expecting wide characters support by attempting to link with libstdc++ while using <iostream> and <regex>
update packaging script w/ new arguments
rewrite ci build pattern to only rewrite core_version.h once per job
restore behaviour from #6414 for other cases
Missing stdbool.h for 'bool' in features .h, at least one user is arduinoWebSockets
Adds minimal headers sanity-check script to verify that C builds work as expected
Also noticed and removed default argument from crc32() in internal .h that may be used in .c
(not sure how extern C & default worked simultaniously, but at least in our .cpp Gcc somehow figured out it is a no overload solution)
