Clean up configure.ac and add workflow_dispatch to tag.yaml

[mlee03]

Description
In this PR, the following have been changed in configure.ac.

• Bug fix: Corrected $RPATHFLAGS to $RPATH_FLAGS
• Dead code removal: Removed the unused variable declarationvariable build_mpi=no
• Style consistency: Replaced bare if/fi shell blocks with AS_IF macros in order to be consistent with the rest of the file.
• Simplified xarray conditional: Replaced an if/else/fi block that called AM_CONDITIONAL in both branches with a single unconditional AM_CONDITIONAL call.
• Indentation fixes: Corrected unindented macro calls inside several AS_IF bodies statements.
• Minor: Added missing [] quoting around AC_MSG_WARN arguments; removed a stray leading space from a comment; removed a spurious space before dnl on AC_SUBST(RPATH_FLAGS).

Disclaimer: AI coding assistant was used to generate and implement solutions to the #402, and to write the initial draft of this PR summary

Fixes #402

How Has This Been Tested?
NA

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[ceblanton]

Thank you! I had to use AI to interpret both commits ha ha but they look great. Let's see if the manual dispatch works!

[rem1776]

Looks like good changes to me

[underwoo]

I know you didn't add this, but other compilers support openACC. This message should be changed. Introduction to OpenACC — OpenACC/CUDA for beginners https://enccs.github.io/OpenACC-CUDA-beginners/1.02_openacc-introduction/

Also, should configure fail if the user requested openACC,and configure was unable to find the header?

I understand this is outside the scope of this change, but these are things that should be addressed. Open new issues if these will be addressed outside this PR.

[underwoo]

Wouldn't it be better to search the compiler option space for the openACC option? Otherwise, the user will need to add to the [CF]FLAGS to compile with openACC.

[underwoo]

Is the only GPU support openACC? If so, the configure option should be changed to reflect that. Enable-openacc instead of enable-gpu