Code Blocks/Eclipse: Use non-default stdlib includes when specified.

When -stdlib=x is specified in CMAKE_CXX_FLAGS this passes it along so
that the correct include dirs are detected.
Code Blocks/Eclipse: Add -std= flag matching.

When -std=x is specified in CMAKE_CXX_FLAGS this passes it along.
Merge topic 'extra-generators-std-flags' into next

eaf6f67f Code Blocks/Eclipse: Add -std= flag matching.
45a25d63 Code Blocks/Eclipse: Use non-default stdlib includes when specified.