-dnl eval is necessary to expand ac_cpp.
-dnl Ultrix and Pyramid sh refuse to redirect output of eval, so use subshell.
+ dnl AIX "xlc -E" and "cc -E" omit #line directives for header files
+ dnl that contain only a #include of other header files and no
+ dnl non-comment tokens of their own. This leads to a failure to
+ dnl detect the absolute name of <dirent.h>, <signal.h>, <poll.h>
+ dnl and others. The workaround is to force preservation of comments
+ dnl through option -C. This ensures all necessary #line directives
+ dnl are present. GCC supports option -C as well.
+ case "$host_os" in
+ aix*) gl_absname_cpp="$ac_cpp -C" ;;
+ *) gl_absname_cpp="$ac_cpp" ;;
+ esac
+ dnl eval is necessary to expand gl_absname_cpp.
+ dnl Ultrix and Pyramid sh refuse to redirect output of eval,
+ dnl so use subshell.