AIX bug in Makefile - find with -not #24634

Noticed this the other day when testing the proposed SKIP_XZ feature. Running make on AIX complains when running make now because there is a find with a -not which is apparently not supported. It was first introduced in eebcb48, which is a year ago. It's not fatal, but it errors when you start make and lint-md won't work properly because of it.

LINT_MD_MISC_FILES := $(shell find $(LINT_MD_TARGETS) -type f \
  -not -path '*node_modules*' -not -path 'test/fixtures/*' -name '*.md') \
  $(LINT_MD_ROOT_DOCS)

The error shows up in every run if you look at the console output, e.g. the latest one right now @ https://ci.nodejs.org/job/node-test-commit-aix/nodes=aix61-ppc64/19164/consoleFull:

15:41:59 + gmake run-ci -j 5
15:41:59 find: 0652-017 -not is not a valid option.
15:41:59 python ./configure --verbose  --dest-cpu=ppc64

Low priority I suppose. Over to the IBM folks.