Please find attached the patch and a ChangeLog entry. This is my first 
patch, apologies for any mistakes in the submission process.

This patch is the simple removal of an OPT_dec_structure case from a 
switch statement, it was noticeable as there was no corresponding code 
for the other dec specific options. I spotted this before the creation 
of PR fortran/87919 so I now know that this fixes the broken behaviour 
of -fno-dec-structure.

The patch contains a change to gcc/fortran/options.c and four testcases 
pr87919-dec-structure-*.f where * is one of 1, 2, 3 and 4.

The testcases are specified to compile with no specific options, -fdec, 
-fdec-structure and both -fdec and -fno-dec-structure.

After building the compiler on x86_64 I got the following results 
aggregated from make -j 5 check-fortran:

 Â Â Â  Â Â Â  === gfortran Summary ===

# of expected passesÂ Â Â  Â Â Â  48184
# of expected failuresÂ Â Â  Â Â Â  103
# of unsupported testsÂ Â Â  Â Â Â  79


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