test: POSIX, stop FD_Fail to fail

In our build environments, /etc/fstab is an empty file. Use /etc/mtab,
which should be non-empty anywhere, hopefully.

For the reference, the test fails as follows:
FAIL: KLEE :: Runtime/POSIX/FD_Fail.c (188 of 212)
************ TEST 'KLEE :: Runtime/POSIX/FD_Fail.c' FAILED ************
Script:
--
clang-3.8 -Iinclude test/Runtime/POSIX/FD_Fail.c -emit-llvm -O0 -c -o build/test/Runtime/POSIX/Output/FD_Fail.c.tmp1.bc
rm -rf build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.klee-out
build/bin/klee --output-dir=build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.klee-out --libc=uclibc --posix-runtime build/test/Runtime/POSIX/Output/FD_Fail.c.tmp1.bc --sym-files 0 0 --max-fail 1 > build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.log
grep -q "fread(): ok" build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.log
grep -q "fread(): fail" build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.log
grep -q "fclose(): ok" build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.log
grep -q "fclose(): fail" build/test/Runtime/POSIX/Output/FD_Fail.c.tmp.log
--
Exit Code: 1

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>

0 files changed, 0 insertions, 0 deletions