Add fallback compiler settings equivalent to gcc default

[hughcars]

My ubuntu vended /usr/bin/cc fails in the vendor check because it's a wrapper of gcc:

/usr/bin/cc --version
cc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

resulting in flags not being set correctly. This PR adds a gcc-equivalent default for the relevant flags (given parsing ( or ) within Makefile is tricky, so can't search for just Ubuntu). These flags are then overridden for specific compilers when necessary. Should preserve the "only set if not explicitly set" behaviour and detects against any other wrappers around gcc-equivalent compilers. If a future compiler vendor needs to be supported, should just need another if branch.

Note: this was being encountered for libceed builds nested within Palace builds as part of a spack build (which was using /usr/bin/cc).

Before the change:

make VERBOSE=1
make: 'lib' with optional backends: /cpu/self/memcheck/serial /cpu/self/memcheck/blocked
/usr/bin/cc -I./include -O        -c -o build/interface/ceed-basis.o 

after the change:

make VERBOSE=1
make: 'lib' with optional backends: /cpu/self/memcheck/serial /cpu/self/memcheck/blocked /cpu/self/avx/serial /cpu/self/avx/blocked
/usr/bin/cc -I./include -O -march=native -g -ffp-contract=fast -fopenmp-simd -fPIC -std=c99 -Wall -Wextra -Wno-unused-parameter -MMD -MP    -c -o build/interface/ceed-basis.o

[jeremylt]

It makes sense to me, but @jedbrown may have some thoughts as he's done more work on the Makefile

[jedbrown]

Thanks for this PR. One consequence of moving from declarative to imperative (with conditionals) is that one needs to read through all the conditional logic (or run on the target machine) to determine how it would be configured; cf. make print-CFLAGS.clang. I think the issue you observed could be addressed within the declarative model by updating these two lines. What do you think?

CC_VENDOR := $(firstword $(filter gcc (GCC) cc clang icc icc_orig oneAPI XL emcc,$(subst -, ,$(shell $(CC) --version))))
CC_VENDOR := $(subst cc,gcc,$(subst (GCC),gcc,$(subst icc_orig,icc,$(CC_VENDOR))))

[hughcars]

Thanks for this PR. One consequence of moving from declarative to imperative (with conditionals) is that one needs to read through all the conditional logic (or run on the target machine) to determine how it would be configured; cf. make print-CFLAGS.clang. I think the issue you observed could be addressed within the declarative model by updating these two lines. What do you think?

CC_VENDOR := $(firstword $(filter gcc (GCC) cc clang icc icc_orig oneAPI XL emcc,$(subst -, ,$(shell $(CC) --version))))
CC_VENDOR := $(subst cc,gcc,$(subst (GCC),gcc,$(subst icc_orig,icc,$(CC_VENDOR))))

Thank you for the review. I didn't appreciate that usage of make print. I played around with a few attempts at doing something like that, but found the nested function calls increasingly confusing to read. For example that particular one doesn't work if using gcc:

CC_VENDOR := $(firstword $(filter gcc (GCC) cc clang icc icc_orig oneAPI XL emcc,$(subst -, ,$(shell $(CC) --version))))
$(info CC_VENDOR ${CC_VENDOR})
CC_VENDOR := $(subst cc,gcc,$(subst (GCC),gcc,$(subst icc_orig,icc,$(CC_VENDOR))))
$(info CC_VENDOR ${CC_VENDOR})

prints gcc then ggcc for example. If you'd rather a means of setting CC_VENDOR and leaving the rest untouched though, I can put that together. For instance if a callout to sed is permissable, there's a reasonably clean solution to the ( issue.

Alternatively

CC_VENDOR := $(subst ggcc,gcc,$(subst cc,gcc,$(subst (GCC),gcc,$(subst icc_orig,icc,$(CC_VENDOR)))))

undoes the above, but leaves the igcc issue.

[hughcars]

As a more minimalist approach, with the same gcc style fallback, and maintaining the XXX.$(CC_VENDOR) variables:

CC_VENDOR := $(firstword $(filter gcc (GCC) clang icc icc_orig oneAPI XL emcc,$(subst -, ,$(shell $(CC) --version))))
CC_VENDOR := $(subst (GCC),gcc,$(subst icc_orig,icc,$(CC_VENDOR)))
CC_VENDOR := $(if $(CC_VENDOR),$(CC_VENDOR),gcc)

[hughcars]

I updated to only map cc -> gcc for an exact match. Opted for a new line over a one liner for readability, given $(CC_VENDOR) is used twice.

[jedbrown]

LGTM, thanks.

[jeremylt]

@hughcars I think this is good to merge unless you have any other changes, yes?