Makefile.subdirs: don't assign ; to DEPFLAGS[123] / QUIET_{CC,CXX}

[fingolfin]

I believe this fixes #1007 but have not yet verified so (will do next)

[wbhart]

Seems to work locally, though I am not clear why the semicolons are required (and clearly ok) on the prior lines, but not on these lines.

[wbhart]

If this passes, I'll issue 2.8.2 with this fix.

[wbhart]

I wonder if the problem was actually the spaces instead of tabs.

[fingolfin]

I've verified that this patch fixes the compilation issues on Yggdrasil, see JuliaPackaging/Yggdrasil#3750 and the build logs there.

[wbhart]

Thanks, that's very helpful. I'll wait for CI to verify the fix here on GitHub and I'll issue the release.

I ended up making the changes by hand locally rather than merging this PR, since I did the release paperwork in the same commit.