custom FETCHCONTENT_BASE_DIR bug fix

[pefedotov]

Fixes a bug related to incorrect paths when automatically loading hwloc.

If the path for downloaded projects is FETCHCONTENT_BASE_DIR
has been changed, then the existing cmake script points to a non-existent folder, since hwloc will be loaded to another location.

[jenkins-cscs]

Can one of the admins verify this patch?

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.12%	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (049b935)	222123	188895	85.04%
Head commit (0887421)	191107 (-31016)	162749 (-26146)	85.16% (+0.12%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6513)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[hkaiser]

Also, please address the cmake-format issue reported (see https://gist.github.com/hkaiser/debb4ce2e5cf64722db0f49c90cee01a)

[pefedotov]

Since cmake does not provide a single variable for all occasions, I decided to create a condition. If a special path was specified, then use it, otherwise, what was initially specified in the code (default path).

[hkaiser]

LGTM, thanks!

[hkaiser]

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