Sorry for the late response.
I am using Code::Blocks 17.12, LLVM 6.0.0-Win64.
Both are installed into sub-folders of E:\Compilers, because I hate installing things to my C-drive and avoid it when possible.
BlueHazzard: I was not aware that "Save Everything" was necessary to save global compiler settings, but it doesn't help anyway.
stahta01: Putting " " in the Link Library slot causes it to put quotes around the full file name and search for " kernel32.lib", etc., which it can't find.
Following oBFusCATed's suggestion, I tracked down "default.conf" in "\AppData\Roaming\CodeBlocks".
When the Link Library: value is set to -something, there's a few lines in the compiler's <switches> set:
<LINK>
<str>
<![CDATA[-something]]>
</str>
</LINK>
When the Link Library: value is absent, the <LINK>...</LINK> lines do not exist.
If I paste in
<LINK>
<str>
<![CDATA[]]>
</str>
</LINK>
The linking "works" (Inasmuch as I'm still working out how to get CLang/LLVM to compile and link, but that's not a Code::Blocks problem.)
When I quit, however, it rewrites the default.conf file to remove the <LINK>...</LINK> lines and I get the error on the next run.
So:
A resolution for this bug would be fore Code::Blocks to include the empty switches in the default.conf as above.