Cleans up all warnings seen w/GCC 9.1 to allow it to track the main
branch more easily until 3.x.
Does not include Ticker.h "fix" of pragmas around a function cast we're
doing that GCC9 doesn't like, that will be addressed separately and
maybe only in the 3.0 branch.
Does not include GDB hook fix, either, because the pragmas required
to disable the GCC9.1 warnings don't exist in 4.8 at all.
* Use newlib libc library
This change adds libcmin.a, which is created from newlib libc by selectively removing some of the object files (mostly related to heap management).
The list of files is available in tools/sdk/lib/make_libcmin.sh. Files which are not needed are commented out.
This change adds support for various functions which were missing, like sscanf, strftime, etc.
* Fix some of the time functions
* Redirect stdout to serial
* Implement __putc_r
* Switch to custom newlib build
Built from https://github.com/igrr/newlib-xtensa using:
./configure --with-newlib --enable-multilib --disable-newlib-io-c99-formats --enable-newlib-supplied-syscalls --enable-target-optspace --program-transform-name="s&^&xtensa-lx106-elf-&" --disable-option-checking --with-target-subdir=xtensa-lx106-elf --target=xtensa-lx106-elf --enable-newlib-nano-formatted-io --enable-newlib-reent-small --prefix=path-to-arduino-core/tools/sdk/libc
CROSS_CFLAGS="-DMALLOC_PROVIDED -DSIGNAL_PROVIDED -DABORT_PROVIDED" make
make install
* Update tests
