fix(build): check features before mangling CFLAGS

[aws-nslick]

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fix(build): check features before mangling CFLAGS

Yet another autotools fix: If any warning/devel CFLAGS would invoke warnings in headers used to detect dependencies, those dependencies will fail with a highly misleading/confusing error message:

configure: Found .git directory. Adding -Werror to CFLAGS. checking if running on EC2 instance... yes checking if want AWS platform optimizations... yes checking for Libfabric 1.18.0 or later... no configure: error: On AWS platforms, Libfabric 1.18.0 or later is required

ie: it is not that Libfabric 1.18 was not found, it was that its headers produced warnings. Fix this by resolving all dependencies before modifying CFLAGS.

[aws-nslick]

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