fix elif preprocessing, I believe

[JorgeG94]

This fixes issue #1195

[perazz]

Thank you for this PR @JorgeG94. I believe it would be worthwhile to add a test routine for #elif cases in https://github.com/fortran-lang/fpm/blob/main/test/fpm_test/test_source_parsing.f90

[JorgeG94]

Thank you for this PR @JorgeG94. I believe it would be worthwhile to add a test routine for #elif cases in https://github.com/fortran-lang/fpm/blob/main/test/fpm_test/test_source_parsing.f90

of course, I was enthralled that I fixed it that I just opened the PR. Let me tend to this

[perazz]

Unfortunately, fpm does not contain a full C preprocessor or even a source parser. A good approach for now is to add capability at user need

[JorgeG94]

Unfortunately, fpm does not contain a full C preprocessor or even a source parser. A good approach for now is to add capability at user need

Excellent, I am writing the test now I shall push it in a second :)

[JorgeG94]

@perazz I've extended the current test. Is this preferred or should I create two new unit tests, one for ifdef + elif and one for ifdef + elif + else ?

[JorgeG94]

I thought about and one test per case is a better practice