[SCons] add AR config option (e.g. to set llvm-ar instead of ar)

[band-a-prend]

Changes proposed in this pull request

Some systems that are based on Clang/LLVM configurations could rely on llvm-ar archiver instead of ar to package static libraries. The proposed tiny patch offers additional config option (like CC, CXX) to allow user to set appropeate prefered AR variable.

Please refer Gentoo Linux issue: https://bugs.gentoo.org/773541

If applicable, fill in the issue number this pull request is fixing

Closes # None

If applicable, provide an example illustrating new features this pull request is introducing

For build and tests of proposed feature the following common SCons configuration was used:

debug="no" 
f90_interface=y 
python_package=full 
python_cmd=python3.10 
optimize_flags="-Wno-inline" 
renamed_shared_libraries="no" 
use_pch="no" 
system_fmt="y" 
system_eigen="y" 
system_yamlcpp="y" 
env_vars="all" 
extra_inc_dirs="/usr/include/eigen3" 
prefix="/usr

The additional alternate options will be mentioned in appropreate cases.
The system Sundials 6.5.0 was used until test with sundials from Cantera submodule (Sundials 5.3.0)
The gfortran always is used to build f90_interface
The cantera.conf was removed before each build run!

Please notice the example of archiver call (ar or llvm-ar):

1. Case: system_sundials="y" system_blas_lapack=n (lapack support is disabled)

ar rc build/lib/libcantera.a build/src/base/AnyMap.os ...

scons -j4 test
...
Tests passed: 4830
Up-to-date tests skipped: 0
Tests failed: 0

2. Case: system_sundials="y" system_blas_lapack=y blas_lapack_libs="blas,lapack"

ar rc build/lib/libcantera.a build/src/base/AnyMap.os ...

scons -j4 test
...
Tests passed: 4830
Up-to-date tests skipped: 0
Tests failed: 0

3. Case: AR=llvm-ar CC=clang CXX=clang++ system_sundials="y" system_blas_lapack=n (lapack support is disabled)

    ...
    AR = 'llvm-ar'
    CC = 'clang'
    CXX = 'clang++'
    ...

llvm-ar rc build/lib/libcantera.a build/src/base/AnyMap.os ...

scons -j4 test
...
Tests passed: 4830
Up-to-date tests skipped: 0
Tests failed: 0

4. Case: AR=llvm-ar CC=clang CXX=clang++ system_sundials="y" system_blas_lapack=y blas_lapack_libs="blas,lapack"

    ...
    AR = 'llvm-ar'
    CC = 'clang'
    CXX = 'clang++'
    ...

llvm-ar rc build/lib/libcantera.a build/src/base/AnyMap.os ...

scons -j4 test
...
Tests passed: 4830
Up-to-date tests skipped: 0
Tests failed: 0

5. Case: AR=llvm-ar CC=clang CXX=clang++ system_sundials="n" system_blas_lapack=y blas_lapack_libs="blas,lapack"

    ...
    AR = 'llvm-ar'
    CC = 'clang'
    CXX = 'clang++'
    ...
    system_sundials = 'n'
...
    CT_SUNDIALS_VERSION                 53
...

llvm-ar rc build/lib/libcantera.a build/ext/sundials/src/sundials/sundials_band.os ...

scons -j4 test
...
Tests passed: 4830
Up-to-date tests skipped: 0
Tests failed: 0

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[ischoegl]

Proposed changes look good to me.

[codecov]

Codecov Report

Merging #1424 (342521e) into main (1fa20b7) will decrease coverage by 0.26%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1424      +/-   ##
==========================================
- Coverage   70.84%   70.59%   -0.26%     
==========================================
  Files         376      376              
  Lines       54784    54781       -3     
  Branches    18137    18137              
==========================================
- Hits        38813    38671     -142     
- Misses      13506    13599      +93     
- Partials     2465     2511      +46     

Impacted Files	Coverage Δ
include/cantera/kinetics/InterfaceKinetics.h	28.57% <0.00%> (-57.15%)	⬇️
include/cantera/kinetics/ReactionRateDelegator.h	71.42% <0.00%> (-19.05%)	⬇️
src/kinetics/Reaction.cpp	68.33% <0.00%> (-11.81%)	⬇️
src/kinetics/KineticsFactory.cpp	81.81% <0.00%> (-10.19%)	⬇️
...terfaces/dotnet/Cantera/src/Interop/InteropUtil.cs	60.75% <0.00%> (-8.87%)	⬇️
include/cantera/kinetics/InterfaceRate.h	81.92% <0.00%> (-6.03%)	⬇️
include/cantera/kinetics/TwoTempPlasmaRate.h	94.73% <0.00%> (-5.27%)	⬇️
include/cantera/kinetics/Falloff.h	78.22% <0.00%> (-3.23%)	⬇️
include/cantera/base/FactoryBase.h	68.75% <0.00%> (-3.13%)	⬇️
src/kinetics/Falloff.cpp	78.00% <0.00%> (-2.99%)	⬇️
... and 11 more

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[band-a-prend]

Thanks!