The nixio library can mistakenly build without shadow password support due to the
compile-time test failing.
Because the test for HAS_SHADOW in the nixio Makefile uses the default CC flags,
the test may attempt to cross-compile with different VFP abi than libc does and
will therefore not link. Passing CCFLAGS on the command line builds the test
correctly and will enable HAS_SHADOW if available.
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