DFLAGS being included per project dependency

[MrcSnm]

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Dflags is being included recursively when the same dependency is included in the same project, which can cause a great problem:

I have done a module called "d_std" which is my own override for phobos. On it I used the dflags:

"dflags": [
		"-mtriple=armv7a-unknown-unknown",
		"-mcpu=cortex-a9",
		"-g",
		"-float-abi=hard",
		"-O0",
		"--boundscheck=off",
		"--relocation-model=static",
		"-fthread-model=local-exec"
	],

If 6 projects includes that d_std, the compilation command will repeat those dflags 6 times. Which can be a really great problem, specially for --relocation-model which can only be called once.