add support for alternative/deprecated toolchain options

[jfgrimm]

No description provided.

[jfgrimm]

guess we should also consider what we would like to rename; current toolchain options are:

cciscxx
cstd
debug
defaultopt
defaultprec
extra_cflags
extra_cxxflags
extra_f90flags
extra_fcflags
extra_fflags
i8
ieee
loose
lowopt
noopt
openmp
opt
optarch
packed-linker-options
pic
precise
r8
rpath
shared
static
strict
unroll
vectorize
verbose
veryloose

[boegel]

@jfgrimm Can you come up with a table like you did in #4464, following the same policy?

[jfgrimm]

@boegel as usual, suggestions/edits welcome

toolchain	current	proposed
	cciscxx	'default_cc': 'cxx'
	cstd
	debug
	defaultopt	'optim': 'default'
	defaultprec	'precision': 'default'
	extra_cflags
	extra_cxxflags
	extra_f90flags
	extra_fcflags
	extra_fflags
	i8	8_byte_int
	ieee	ieee_754
	loose
	lowopt	'optim': 'low'
	noopt	'optim': None
	openmp
	opt	'optim': 'high'
	optarch	arch_optim
	packed-linker-options	packed_linker_opts
	pic
	precise
	r8	8_byte_real
	rpath
	shared
	static
	strict
	unroll
	vectorize
	verbose
	veryloose	'precision': 'very_loose'
clang	loop-vectorize	loop_vectorize
clang	basic-block-vectorize	basic_block_vectorize
craype	dynamic
craype	mpich-mt	mpich_mt
cuda	cuda_gencode
intelcompilers	oneapi
intelcompilers	oneapi_c_cxx
intelcompilers	oneapi_fortran
mpi	usempi	'default_cc': 'mpi_wrappers'

There are a few sets of boolean toggles that are currently mutually exclusive:

• floating point precision: precise, defaultprec, loose, veryloose
• compiler optimisations: opt, defaultopt , lowopt, noopt
• default compiler ($CC): cciscxx, usempi

where it would probably make sense to combine these into single options with multiple supported values, e.g.:
precision=[very_loose|loose|default|high]
optim=[None|low|default|high]
default_cc=[None|cxx|mpi_wrappers]

of course, this would require some extra changes to accommodate for not being booleans

[Micket]

where it would probably make sense to combine these into single options

agreed

[boegel]

@jfgrimm (probably minor) merge conflict to fix here...

[boegel]

During today's conf call we briefly discussed that next to cstd there should also be a cxx_std, which raises the question: do we stick to cstd, or do we aim for c_std instead? Or do we introduce an extra cxxstd (which I guess violates our not-yet-documented policy to use _ as separator).
Or perhaps there's another even better option?