predefined version for "nogc" option

[a11e99z]

I need function that do one thing if GC enabled and other when 
disabled.

I filled issue about it, but maybe u can show some trick:
how to determine in code that "nogc" is enabled?

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LDC supports command option:
-nogc = Do not allow code that generates implicit garbage 
collector calls.

but I cannot find corresponding predefined version in 
https://dlang.org/spec/version.html#predefined-versions

need to add version LDC_nogc or D_nogc.
the one should be enabled for -betterC too.