Cause autogen.sh to fail if autoreconf fails

[pcd1193182]

Description

This change simply detects if autoreconf fails, and if so, causes autogen.sh to fail as well.

Motivation and Context

When doing development, it's possible to forget to add Makefiles or other components to the repository, or to forget to create them at all. If this happens, autoreconf can notice the problem and fail. However, we don't detect this failure. As a result, automated builds will often proceed without knowing anything is wrong, producing obscure and confusing failures later in the build process.

How Has This Been Tested?

This patch has been tested by adding a dependency but not creating the relevant Makefile, and verifying that an automated build fails in a more appropriate place. It has also been tested on builds that should succeed, and it does.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[codecov]

Codecov Report

Merging #7683 into master will decrease coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7683      +/-   ##
==========================================
- Coverage   78.26%   78.09%   -0.17%     
==========================================
  Files         368      368              
  Lines      111801   111801              
==========================================
- Hits        87505    87315     -190     
- Misses      24296    24486     +190

Flag	Coverage Δ
#kernel	78.71% <ø> (+0.04%)	⬆️
#user	67.08% <ø> (-0.43%)	⬇️

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