LFortran: Remove hard-coded --generate-object-code flag

This was added in !9188 (merged) because it is needed for cases covered by CMake's Fortran tests. However, it does not work with Fortran modules and breaks lfortran's own examples/project1. Move the flag to the test cases that need it, just as the original MR did with --implicit-interface.

Original Description

Compilation with --generate-object-code flag is responsible for the build failure described in [1]. This flag is better passed via the CMAKE_Fortran_FLAGS variable to avoid overriding essential compiler behavior.

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1091023.

Fixes: #26597 (closed)
Co-authored-by: @brad.king
Backport: release
Topic-rename: lfortran-generate-object-code