convert gflow.c to D

[WalterBright]

No description provided.

[dlang-bot]

Thanks for your pull request, @WalterBright!

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[WalterBright]

@CyberShadow looks like a problem with CyberShadow/DAutoTest :

Test the D Language specification
../dmd/generated/linux/release/64/dmd -run tools/dspec_tester.d --compiler=../dmd/generated/linux/release/64/dmd
/usr/bin/ld: final link failed: No space left on device
collect2: error: ld returned 1 exit status
Error: linker exited with status 1
posix.mak:811: recipe for target 'test_dspec' failed

[wilzbach]

Isn't this change unrelated?

[WalterBright]

No. I set it to C to avoid name mangling issues with vec_t which is our annoying friend size_t.

[wilzbach]

This is already defined in gdag.d - why not import it (or move it to a common bit)?

[WalterBright]

Because the 'header' files are a mess at the moment, and I decided to defer dealing with that. My goal is to do the least disruptive thing to get the files converted to D. Then, start doing refactoring and removing technical debt.