Rework Fortran configure to allow cross compile overrides

[byrnHDF]

Another possibility using defaults and toolchain file could overwrite.
See #5709 and #5718

The expectation is that cross-compiling will use a toolchain file to provide the correct values.
The defaults are only one way to provide defaults for a specific compiler.

NOTE: The supplied toolchain and Fortran pre-gen files are specific for mingw/gfortran - each platform/compiler will need to supply its own set of files/values.

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Important

Rework HDF5UseFortran.cmake to support cross-compilation by providing default KINDs and sizes.

• Behavior:
  • Modify HDF5UseFortran.cmake to handle cross-compilation by providing default KINDs and sizes when CMAKE_CROSSCOMPILING is true.
  • Default values for INTEGER and REAL KINDs and their sizes are set when cross-compiling.
  • Error messages are adjusted to reflect cross-compilation scenarios.
• Logic:
  • Conditional checks added for CMAKE_CROSSCOMPILING to determine if default values should be used.
  • Default values include INTEGER KINDs {1,2,4,8,16} and REAL KINDs {4,8,10,16}.
  • Default sizes for native kinds are set to 4 for INTEGER and REAL, and 8 for DOUBLE PRECISION when cross-compiling.
• Misc:
  • Adjustments to verbose messages to indicate when defaults are used during cross-compilation.

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[byrnHDF]

The mingw cross-compile gets past the configure stage and then chokes on:
FAILED: [code=1] fortran/src/CMakeFiles/H5_buildiface.dir/H5_buildiface.F90.obj
FAILED: [code=1] fortran/src/CMakeFiles/H5match_types.dir/H5match_types.c.obj

because the values from the defaults are not correctly formatted. Once the syntax is correct then we can update the toolchain with the correct values.

[byrnHDF]

Potential issue: These defaults may not work for all compilers

The requirement is to specify the correct values in a toolchain file. gfortran defaults are just in case.
The other choice is to halt the config if cross-compile is indicated and no values are provided.

[brtnfld]

Where is CROSSCOMPILING_PATH defined?

[byrnHDF]

toolchain defines CROSSCOMPILING_PATH or it must be on the command line.