cmake: CompilerChecks: Correct standard warnings

If the -std options don't work for the compiler, issue a
warning, not an error.  The existing error was not using
a valid message type.
Merge pull request #1290 from rleigh-dundee/cmake-errormsg

cmake: CompilerChecks: Correct standard warnings
Update auto-generated documentation

Repository: openmicroscopy/bioformats
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Generated by BIOFORMATS-5.1-latest-docs-autogen#127 (http://ci.openmicroscopy.org/job/BIOFORMATS-5.1-latest-docs-autogen/127/)