Previously it was 1024 bytes, which occasionally ran into a stack
overflow. I hope that 2048 bytes will be enough for most purposes.
I've also removed some 2048-byte stack size settings in JSON files,
which are unnecessary now that the parent (cortex-m.json) sets them.
The -Qunused-arguments flag disables the warning where some flags are
not relevant to a compilation. This commonly happens when compiling
assembly files (.s or .S files) because some flags are specific to C and
not relevant to assembly.
Because practically all baremetal targets need some form of assembly,
this flag is added to most CFlags. This creates a lot of noise. And it
is also added for compiling C code where it might hide bugs (by hiding
the fact a flag is actually unused).
This commit adds the flag to all assembly compilations and removes them
from all target JSON files.
