Fix PaX/GrSecurity runtime error regression

Commit 8780c53961e668211682d40ad36946294c3145d8 reintroduced an
autotools check that is incompatible with the PaX/GrSecurity dialect of
C. This caused autotools checks to exhibit silent failures that
manifested as NULL pointer exceptions during runtime. A bug report
involving this was submitted to the gentoo bug tracker:

https://bugs.gentoo.org/show_bug.cgi?id=457176

This patch adapts the dirty inode check reintroduced by commit
8780c53961e668211682d40ad36946294c3145d8 to be semantically valid in the
PaX/GrSecurity dialect of C.

Reported-by: Marcin Mirosław <bug@mejor.pl>
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>