When '$(PREFIX)objdump' is not present fallback to native '(g)objdump'.
'objdump' is used when flashing for some boards but the toolchain may
not be installed when building in docker.
This will allow using 'objdump' in 'cpu/kinetis/dist/check-fcfield.sh'.
`command -v first second third` only works in `bash` and not in `sh`.
So replace with multiple calls to `command`.
This fixes using `objcopy` when the toolchain `objcopy` is not available.
This variable can be used to specify the linker which should be used to
link C++ object files. This is needed in order to use g++ for linking
with TOOLCHAIN=llvm.
- Merge flash and flash-elf commands since they were identical except
for the file name of the image
- Split GDB command from DBG environment variable to allow more easily
configure front-ends for GDB via environment variables.
- Remove verbose tests of empty variables and replace by `: ${VAR:=default}`
- Remove passed command line arguments to sub-functions, they were
unused in the functions anyway.
- Remove TUI variable, use `export DBG_EXTRA_FLAGS=-tui` to get the same
result.
