Address minor portability issues

[dankm]

Address some minor annoyances when building on FreeBSD (and possibly other systems):

Use $(MAKE) instead of "make" when determining the GNU Make version
Add OS specific sed for FreeBSD

[codecov-io]

Codecov Report

Merging #9414 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9414      +/-   ##
==========================================
- Coverage   41.51%   41.48%   -0.03%     
==========================================
  Files         569      569              
  Lines       74322    74322              
==========================================
- Hits        30855    30835      -20     
- Misses      39627    39646      +19     
- Partials     3840     3841       +1

Impacted Files	Coverage Δ
services/pull/check.go	48.59% <0%> (-10.57%)	⬇️
modules/indexer/code/indexer.go	44.73% <0%> (-10.53%)	⬇️
modules/repository/repo.go	33.55% <0%> (-1.98%)	⬇️
modules/migrations/migrate.go	24.21% <0%> (-1.58%)	⬇️
models/webhook.go	69.39% <0%> (-1.07%)	⬇️
models/repo_list.go	73.14% <0%> (-0.93%)	⬇️
modules/migrations/gitea.go	9.03% <0%> (-0.64%)	⬇️
models/repo.go	48.2% <0%> (+0.1%)	⬆️
models/error.go	33.2% <0%> (+1.11%)	⬆️
modules/task/migrate.go	28.94% <0%> (+3.94%)	⬆️
... and 1 more

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