CheckStructHasMember: avoid breakage on -Wall -Werror (#15203)

With CMAKE_C_FLAGS='-Wall -Werror', this test breaks due to
-Werror=unused-value. Fix this by ignoring the return value.
Fix some spelling errors in comments
Merge topic 'fix-comment-typos'

bef23e81 Fix some spelling errors in comments
Merge topic 'CheckStructHasMember-avoid-breakage-on-Wall'

384d3ce7 CheckStructHasMember: avoid breakage on -Wall -Werror (#15203)
Help: Drop development topic notes to prepare release

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CMake 3.1.0-rc1 version update
Merge branch 'release'
Begin post-3.1 development
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